three.js/examples/jsm/loaders/GLTFLoader.js

import {
	AnimationClip,
	Bone,
	Box3,
	BufferAttribute,
	BufferGeometry,
	ClampToEdgeWrapping,
	Color,
	DirectionalLight,
	DoubleSide,
	FileLoader,
	FrontSide,
	Group,
	ImageBitmapLoader,
	InterleavedBuffer,
	InterleavedBufferAttribute,
	Interpolant,
	InterpolateDiscrete,
	InterpolateLinear,
	Line,
	LineBasicMaterial,
	LineLoop,
	LineSegments,
	LinearFilter,
	LinearMipmapLinearFilter,
	LinearMipmapNearestFilter,
	Loader,
	LoaderUtils,
	Material,
	MathUtils,
	Matrix4,
	Mesh,
	MeshBasicMaterial,
	MeshPhysicalMaterial,
	MeshStandardMaterial,
	MirroredRepeatWrapping,
	NearestFilter,
	NearestMipmapLinearFilter,
	NearestMipmapNearestFilter,
	NumberKeyframeTrack,
	Object3D,
	OrthographicCamera,
	PerspectiveCamera,
	PointLight,
	Points,
	PointsMaterial,
	PropertyBinding,
	Quaternion,
	QuaternionKeyframeTrack,
	RGBFormat,
	RepeatWrapping,
	Skeleton,
	SkinnedMesh,
	Sphere,
	SpotLight,
	TangentSpaceNormalMap,
	Texture,
	TextureLoader,
	TriangleFanDrawMode,
	TriangleStripDrawMode,
	Vector2,
	Vector3,
	VectorKeyframeTrack,
	sRGBEncoding
} from '../../../build/three.module.js';

class GLTFLoader extends Loader {

	constructor( manager ) {

		super( manager );

		this.dracoLoader = null;
		this.ktx2Loader = null;
		this.meshoptDecoder = null;

		this.pluginCallbacks = [];

		this.register( function ( parser ) {

			return new GLTFMaterialsClearcoatExtension( parser );

		} );

		this.register( function ( parser ) {

			return new GLTFTextureBasisUExtension( parser );

		} );

		this.register( function ( parser ) {

			return new GLTFTextureWebPExtension( parser );

		} );

		this.register( function ( parser ) {

			return new GLTFMaterialsSheenExtension( parser );

		} );

		this.register( function ( parser ) {

			return new GLTFMaterialsTransmissionExtension( parser );

		} );

		this.register( function ( parser ) {

			return new GLTFMaterialsVolumeExtension( parser );

		} );

		this.register( function ( parser ) {

			return new GLTFMaterialsIorExtension( parser );

		} );

		this.register( function ( parser ) {

			return new GLTFMaterialsSpecularExtension( parser );

		} );

		this.register( function ( parser ) {

			return new GLTFLightsExtension( parser );

		} );

		this.register( function ( parser ) {

			return new GLTFMeshoptCompression( parser );

		} );

	}

	load( url, onLoad, onProgress, onError ) {

		const scope = this;

		let resourcePath;

		if ( this.resourcePath !== '' ) {

			resourcePath = this.resourcePath;

		} else if ( this.path !== '' ) {

			resourcePath = this.path;

		} else {

			resourcePath = LoaderUtils.extractUrlBase( url );

		}

		// Tells the LoadingManager to track an extra item, which resolves after
		// the model is fully loaded. This means the count of items loaded will
		// be incorrect, but ensures manager.onLoad() does not fire early.
		this.manager.itemStart( url );

		const _onError = function ( e ) {

			if ( onError ) {

				onError( e );

			} else {

				console.error( e );

			}

			scope.manager.itemError( url );
			scope.manager.itemEnd( url );

		};

		const loader = new FileLoader( this.manager );

		loader.setPath( this.path );
		loader.setResponseType( 'arraybuffer' );
		loader.setRequestHeader( this.requestHeader );
		loader.setWithCredentials( this.withCredentials );

		loader.load( url, function ( data ) {

			try {

				scope.parse( data, resourcePath, function ( gltf ) {

					onLoad( gltf );

					scope.manager.itemEnd( url );

				}, _onError );

			} catch ( e ) {

				_onError( e );

			}

		}, onProgress, _onError );

	}

	setDRACOLoader( dracoLoader ) {

		this.dracoLoader = dracoLoader;
		return this;

	}

	setDDSLoader() {

		throw new Error(

			'THREE.GLTFLoader: "MSFT_texture_dds" no longer supported. Please update to "KHR_texture_basisu".'

		);

	}

	setKTX2Loader( ktx2Loader ) {

		this.ktx2Loader = ktx2Loader;
		return this;

	}

	setMeshoptDecoder( meshoptDecoder ) {

		this.meshoptDecoder = meshoptDecoder;
		return this;

	}

	register( callback ) {

		if ( this.pluginCallbacks.indexOf( callback ) === - 1 ) {

			this.pluginCallbacks.push( callback );

		}

		return this;

	}

	unregister( callback ) {

		if ( this.pluginCallbacks.indexOf( callback ) !== - 1 ) {

			this.pluginCallbacks.splice( this.pluginCallbacks.indexOf( callback ), 1 );

		}

		return this;

	}

	parse( data, path, onLoad, onError ) {

		let content;
		const extensions = {};
		const plugins = {};

		if ( typeof data === 'string' ) {

			content = data;

		} else {

			const magic = LoaderUtils.decodeText( new Uint8Array( data, 0, 4 ) );

			if ( magic === BINARY_EXTENSION_HEADER_MAGIC ) {

				try {

					extensions[ EXTENSIONS.KHR_BINARY_GLTF ] = new GLTFBinaryExtension( data );

				} catch ( error ) {

					if ( onError ) onError( error );
					return;

				}

				content = extensions[ EXTENSIONS.KHR_BINARY_GLTF ].content;

			} else {

				content = LoaderUtils.decodeText( new Uint8Array( data ) );

			}

		}

		const json = JSON.parse( content );

		if ( json.asset === undefined || json.asset.version[ 0 ] < 2 ) {

			if ( onError ) onError( new Error( 'THREE.GLTFLoader: Unsupported asset. glTF versions >=2.0 are supported.' ) );
			return;

		}

		const parser = new GLTFParser( json, {

			path: path || this.resourcePath || '',
			crossOrigin: this.crossOrigin,
			requestHeader: this.requestHeader,
			manager: this.manager,
			ktx2Loader: this.ktx2Loader,
			meshoptDecoder: this.meshoptDecoder

		} );

		parser.fileLoader.setRequestHeader( this.requestHeader );

		for ( let i = 0; i < this.pluginCallbacks.length; i ++ ) {

			const plugin = this.pluginCallbacks[ i ]( parser );
			plugins[ plugin.name ] = plugin;

			// Workaround to avoid determining as unknown extension
			// in addUnknownExtensionsToUserData().
			// Remove this workaround if we move all the existing
			// extension handlers to plugin system
			extensions[ plugin.name ] = true;

		}

		if ( json.extensionsUsed ) {

			for ( let i = 0; i < json.extensionsUsed.length; ++ i ) {

				const extensionName = json.extensionsUsed[ i ];
				const extensionsRequired = json.extensionsRequired || [];

				switch ( extensionName ) {

					case EXTENSIONS.KHR_MATERIALS_UNLIT:
						extensions[ extensionName ] = new GLTFMaterialsUnlitExtension();
						break;

					case EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS:
						extensions[ extensionName ] = new GLTFMaterialsPbrSpecularGlossinessExtension();
						break;

					case EXTENSIONS.KHR_DRACO_MESH_COMPRESSION:
						extensions[ extensionName ] = new GLTFDracoMeshCompressionExtension( json, this.dracoLoader );
						break;

					case EXTENSIONS.KHR_TEXTURE_TRANSFORM:
						extensions[ extensionName ] = new GLTFTextureTransformExtension();
						break;

					case EXTENSIONS.KHR_MESH_QUANTIZATION:
						extensions[ extensionName ] = new GLTFMeshQuantizationExtension();
						break;

					default:

						if ( extensionsRequired.indexOf( extensionName ) >= 0 && plugins[ extensionName ] === undefined ) {

							console.warn( 'THREE.GLTFLoader: Unknown extension "' + extensionName + '".' );

						}

				}

			}

		}

		parser.setExtensions( extensions );
		parser.setPlugins( plugins );
		parser.parse( onLoad, onError );

	}

}

/* GLTFREGISTRY */

function GLTFRegistry() {

	let objects = {};

	return	{

		get: function ( key ) {

			return objects[ key ];

		},

		add: function ( key, object ) {

			objects[ key ] = object;

		},

		remove: function ( key ) {

			delete objects[ key ];

		},

		removeAll: function () {

			objects = {};

		}

	};

}

/*********************************/
/********** EXTENSIONS ***********/
/*********************************/

const EXTENSIONS = {
	KHR_BINARY_GLTF: 'KHR_binary_glTF',
	KHR_DRACO_MESH_COMPRESSION: 'KHR_draco_mesh_compression',
	KHR_LIGHTS_PUNCTUAL: 'KHR_lights_punctual',
	KHR_MATERIALS_CLEARCOAT: 'KHR_materials_clearcoat',
	KHR_MATERIALS_IOR: 'KHR_materials_ior',
	KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS: 'KHR_materials_pbrSpecularGlossiness',
	KHR_MATERIALS_SHEEN: 'KHR_materials_sheen',
	KHR_MATERIALS_SPECULAR: 'KHR_materials_specular',
	KHR_MATERIALS_TRANSMISSION: 'KHR_materials_transmission',
	KHR_MATERIALS_UNLIT: 'KHR_materials_unlit',
	KHR_MATERIALS_VOLUME: 'KHR_materials_volume',
	KHR_TEXTURE_BASISU: 'KHR_texture_basisu',
	KHR_TEXTURE_TRANSFORM: 'KHR_texture_transform',
	KHR_MESH_QUANTIZATION: 'KHR_mesh_quantization',
	EXT_TEXTURE_WEBP: 'EXT_texture_webp',
	EXT_MESHOPT_COMPRESSION: 'EXT_meshopt_compression'
};

/**
 * Punctual Lights Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_lights_punctual
 */
class GLTFLightsExtension {

	constructor( parser ) {

		this.parser = parser;
		this.name = EXTENSIONS.KHR_LIGHTS_PUNCTUAL;

		// Object3D instance caches
		this.cache = { refs: {}, uses: {} };

	}

	_markDefs() {

		const parser = this.parser;
		const nodeDefs = this.parser.json.nodes || [];

		for ( let nodeIndex = 0, nodeLength = nodeDefs.length; nodeIndex < nodeLength; nodeIndex ++ ) {

			const nodeDef = nodeDefs[ nodeIndex ];

			if ( nodeDef.extensions
					&& nodeDef.extensions[ this.name ]
					&& nodeDef.extensions[ this.name ].light !== undefined ) {

				parser._addNodeRef( this.cache, nodeDef.extensions[ this.name ].light );

			}

		}

	}

	_loadLight( lightIndex ) {

		const parser = this.parser;
		const cacheKey = 'light:' + lightIndex;
		let dependency = parser.cache.get( cacheKey );

		if ( dependency ) return dependency;

		const json = parser.json;
		const extensions = ( json.extensions && json.extensions[ this.name ] ) || {};
		const lightDefs = extensions.lights || [];
		const lightDef = lightDefs[ lightIndex ];
		let lightNode;

		const color = new Color( 0xffffff );

		if ( lightDef.color !== undefined ) color.fromArray( lightDef.color );

		const range = lightDef.range !== undefined ? lightDef.range : 0;

		switch ( lightDef.type ) {

			case 'directional':
				lightNode = new DirectionalLight( color );
				lightNode.target.position.set( 0, 0, - 1 );
				lightNode.add( lightNode.target );
				break;

			case 'point':
				lightNode = new PointLight( color );
				lightNode.distance = range;
				break;

			case 'spot':
				lightNode = new SpotLight( color );
				lightNode.distance = range;
				// Handle spotlight properties.
				lightDef.spot = lightDef.spot || {};
				lightDef.spot.innerConeAngle = lightDef.spot.innerConeAngle !== undefined ? lightDef.spot.innerConeAngle : 0;
				lightDef.spot.outerConeAngle = lightDef.spot.outerConeAngle !== undefined ? lightDef.spot.outerConeAngle : Math.PI / 4.0;
				lightNode.angle = lightDef.spot.outerConeAngle;
				lightNode.penumbra = 1.0 - lightDef.spot.innerConeAngle / lightDef.spot.outerConeAngle;
				lightNode.target.position.set( 0, 0, - 1 );
				lightNode.add( lightNode.target );
				break;

			default:
				throw new Error( 'THREE.GLTFLoader: Unexpected light type: ' + lightDef.type );

		}

		// Some lights (e.g. spot) default to a position other than the origin. Reset the position
		// here, because node-level parsing will only override position if explicitly specified.
		lightNode.position.set( 0, 0, 0 );

		lightNode.decay = 2;

		if ( lightDef.intensity !== undefined ) lightNode.intensity = lightDef.intensity;

		lightNode.name = parser.createUniqueName( lightDef.name || ( 'light_' + lightIndex ) );

		dependency = Promise.resolve( lightNode );

		parser.cache.add( cacheKey, dependency );

		return dependency;

	}

	createNodeAttachment( nodeIndex ) {

		const self = this;
		const parser = this.parser;
		const json = parser.json;
		const nodeDef = json.nodes[ nodeIndex ];
		const lightDef = ( nodeDef.extensions && nodeDef.extensions[ this.name ] ) || {};
		const lightIndex = lightDef.light;

		if ( lightIndex === undefined ) return null;

		return this._loadLight( lightIndex ).then( function ( light ) {

			return parser._getNodeRef( self.cache, lightIndex, light );

		} );

	}

}

/**
 * Unlit Materials Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_unlit
 */
class GLTFMaterialsUnlitExtension {

	constructor() {

		this.name = EXTENSIONS.KHR_MATERIALS_UNLIT;

	}

	getMaterialType() {

		return MeshBasicMaterial;

	}

	extendParams( materialParams, materialDef, parser ) {

		const pending = [];

		materialParams.color = new Color( 1.0, 1.0, 1.0 );
		materialParams.opacity = 1.0;

		const metallicRoughness = materialDef.pbrMetallicRoughness;

		if ( metallicRoughness ) {

			if ( Array.isArray( metallicRoughness.baseColorFactor ) ) {

				const array = metallicRoughness.baseColorFactor;

				materialParams.color.fromArray( array );
				materialParams.opacity = array[ 3 ];

			}

			if ( metallicRoughness.baseColorTexture !== undefined ) {

				pending.push( parser.assignTexture( materialParams, 'map', metallicRoughness.baseColorTexture ) );

			}

		}

		return Promise.all( pending );

	}

}

/**
 * Clearcoat Materials Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_clearcoat
 */
class GLTFMaterialsClearcoatExtension {

	constructor( parser ) {

		this.parser = parser;
		this.name = EXTENSIONS.KHR_MATERIALS_CLEARCOAT;

	}

	getMaterialType( materialIndex ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;

		return MeshPhysicalMaterial;

	}

	extendMaterialParams( materialIndex, materialParams ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

			return Promise.resolve();

		}

		const pending = [];

		const extension = materialDef.extensions[ this.name ];

		if ( extension.clearcoatFactor !== undefined ) {

			materialParams.clearcoat = extension.clearcoatFactor;

		}

		if ( extension.clearcoatTexture !== undefined ) {

			pending.push( parser.assignTexture( materialParams, 'clearcoatMap', extension.clearcoatTexture ) );

		}

		if ( extension.clearcoatRoughnessFactor !== undefined ) {

			materialParams.clearcoatRoughness = extension.clearcoatRoughnessFactor;

		}

		if ( extension.clearcoatRoughnessTexture !== undefined ) {

			pending.push( parser.assignTexture( materialParams, 'clearcoatRoughnessMap', extension.clearcoatRoughnessTexture ) );

		}

		if ( extension.clearcoatNormalTexture !== undefined ) {

			pending.push( parser.assignTexture( materialParams, 'clearcoatNormalMap', extension.clearcoatNormalTexture ) );

			if ( extension.clearcoatNormalTexture.scale !== undefined ) {

				const scale = extension.clearcoatNormalTexture.scale;

				materialParams.clearcoatNormalScale = new Vector2( scale, scale );

			}

		}

		return Promise.all( pending );

	}

}

/**
 * Sheen Materials Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_sheen
 */
class GLTFMaterialsSheenExtension {

	constructor( parser ) {

		this.parser = parser;
		this.name = EXTENSIONS.KHR_MATERIALS_SHEEN;

	}

	getMaterialType( materialIndex ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;

		return MeshPhysicalMaterial;

	}

	extendMaterialParams( materialIndex, materialParams ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

			return Promise.resolve();

		}

		const pending = [];

		materialParams.sheenTint = new Color( 0, 0, 0 );
		materialParams.sheenRoughness = 0;
		materialParams.sheen = 1;

		const extension = materialDef.extensions[ this.name ];

		if ( extension.sheenColorFactor !== undefined ) {

			materialParams.sheenTint.fromArray( extension.sheenColorFactor );

		}

		if ( extension.sheenRoughnessFactor !== undefined ) {

			materialParams.sheenRoughness = extension.sheenRoughnessFactor;

		}

		// TODO sheenColorTexture and sheenRoughnessTexture

		return Promise.all( pending );

	}

}

/**
 * Transmission Materials Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_transmission
 * Draft: https://github.com/KhronosGroup/glTF/pull/1698
 */
class GLTFMaterialsTransmissionExtension {

	constructor( parser ) {

		this.parser = parser;
		this.name = EXTENSIONS.KHR_MATERIALS_TRANSMISSION;

	}

	getMaterialType( materialIndex ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;

		return MeshPhysicalMaterial;

	}

	extendMaterialParams( materialIndex, materialParams ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

			return Promise.resolve();

		}

		const pending = [];

		const extension = materialDef.extensions[ this.name ];

		if ( extension.transmissionFactor !== undefined ) {

			materialParams.transmission = extension.transmissionFactor;

		}

		if ( extension.transmissionTexture !== undefined ) {

			pending.push( parser.assignTexture( materialParams, 'transmissionMap', extension.transmissionTexture ) );

		}

		return Promise.all( pending );

	}

}

/**
 * Materials Volume Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_volume
 */
class GLTFMaterialsVolumeExtension {

	constructor( parser ) {

		this.parser = parser;
		this.name = EXTENSIONS.KHR_MATERIALS_VOLUME;

	}

	getMaterialType( materialIndex ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;

		return MeshPhysicalMaterial;

	}

	extendMaterialParams( materialIndex, materialParams ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

			return Promise.resolve();

		}

		const pending = [];

		const extension = materialDef.extensions[ this.name ];

		materialParams.thickness = extension.thicknessFactor !== undefined ? extension.thicknessFactor : 0;

		if ( extension.thicknessTexture !== undefined ) {

			pending.push( parser.assignTexture( materialParams, 'thicknessMap', extension.thicknessTexture ) );

		}

		materialParams.attenuationDistance = extension.attenuationDistance || 0;

		const colorArray = extension.attenuationColor || [ 1, 1, 1 ];
		materialParams.attenuationTint = new Color( colorArray[ 0 ], colorArray[ 1 ], colorArray[ 2 ] );

		return Promise.all( pending );

	}

}

/**
 * Materials ior Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_ior
 */
class GLTFMaterialsIorExtension {

	constructor( parser ) {

		this.parser = parser;
		this.name = EXTENSIONS.KHR_MATERIALS_IOR;

	}

	getMaterialType( materialIndex ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;

		return MeshPhysicalMaterial;

	}

	extendMaterialParams( materialIndex, materialParams ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

			return Promise.resolve();

		}

		const extension = materialDef.extensions[ this.name ];

		materialParams.ior = extension.ior !== undefined ? extension.ior : 1.5;

		return Promise.resolve();

	}

}

/**
 * Materials specular Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_specular
 */
class GLTFMaterialsSpecularExtension {

	constructor( parser ) {

		this.parser = parser;
		this.name = EXTENSIONS.KHR_MATERIALS_SPECULAR;

	}

	getMaterialType( materialIndex ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;

		return MeshPhysicalMaterial;

	}

	extendMaterialParams( materialIndex, materialParams ) {

		const parser = this.parser;
		const materialDef = parser.json.materials[ materialIndex ];

		if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

			return Promise.resolve();

		}

		const pending = [];

		const extension = materialDef.extensions[ this.name ];

		materialParams.specularIntensity = extension.specularFactor !== undefined ? extension.specularFactor : 1.0;

		if ( extension.specularTexture !== undefined ) {

			pending.push( parser.assignTexture( materialParams, 'specularIntensityMap', extension.specularTexture ) );

		}

		const colorArray = extension.specularColorFactor || [ 1, 1, 1 ];
		materialParams.specularTint = new Color( colorArray[ 0 ], colorArray[ 1 ], colorArray[ 2 ] );

		if ( extension.specularColorTexture !== undefined ) {

			pending.push( parser.assignTexture( materialParams, 'specularTintMap', extension.specularColorTexture ).then( function ( texture ) {

				texture.encoding = sRGBEncoding;

			} ) );

		}

		return Promise.all( pending );

	}

}

/**
 * BasisU Texture Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_basisu
 */
class GLTFTextureBasisUExtension {

	constructor( parser ) {

		this.parser = parser;
		this.name = EXTENSIONS.KHR_TEXTURE_BASISU;

	}

	loadTexture( textureIndex ) {

		const parser = this.parser;
		const json = parser.json;

		const textureDef = json.textures[ textureIndex ];

		if ( ! textureDef.extensions || ! textureDef.extensions[ this.name ] ) {

			return null;

		}

		const extension = textureDef.extensions[ this.name ];
		const source = json.images[ extension.source ];
		const loader = parser.options.ktx2Loader;

		if ( ! loader ) {

			if ( json.extensionsRequired && json.extensionsRequired.indexOf( this.name ) >= 0 ) {

				throw new Error( 'THREE.GLTFLoader: setKTX2Loader must be called before loading KTX2 textures' );

			} else {

				// Assumes that the extension is optional and that a fallback texture is present
				return null;

			}

		}

		return parser.loadTextureImage( textureIndex, source, loader );

	}

}

/**
 * WebP Texture Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/EXT_texture_webp
 */
class GLTFTextureWebPExtension {

	constructor( parser ) {

		this.parser = parser;
		this.name = EXTENSIONS.EXT_TEXTURE_WEBP;
		this.isSupported = null;

	}

	loadTexture( textureIndex ) {

		const name = this.name;
		const parser = this.parser;
		const json = parser.json;

		const textureDef = json.textures[ textureIndex ];

		if ( ! textureDef.extensions || ! textureDef.extensions[ name ] ) {

			return null;

		}

		const extension = textureDef.extensions[ name ];
		const source = json.images[ extension.source ];

		let loader = parser.textureLoader;
		if ( source.uri ) {

			const handler = parser.options.manager.getHandler( source.uri );
			if ( handler !== null ) loader = handler;

		}

		return this.detectSupport().then( function ( isSupported ) {

			if ( isSupported ) return parser.loadTextureImage( textureIndex, source, loader );

			if ( json.extensionsRequired && json.extensionsRequired.indexOf( name ) >= 0 ) {

				throw new Error( 'THREE.GLTFLoader: WebP required by asset but unsupported.' );

			}

			// Fall back to PNG or JPEG.
			return parser.loadTexture( textureIndex );

		} );

	}

	detectSupport() {

		if ( ! this.isSupported ) {

			this.isSupported = new Promise( function ( resolve ) {

				const image = new Image();

				// Lossy test image. Support for lossy images doesn't guarantee support for all
				// WebP images, unfortunately.
				image.src = 'data:image/webp;base64,UklGRiIAAABXRUJQVlA4IBYAAAAwAQCdASoBAAEADsD+JaQAA3AAAAAA';

				image.onload = image.onerror = function () {

					resolve( image.height === 1 );

				};

			} );

		}

		return this.isSupported;

	}

}

/**
 * meshopt BufferView Compression Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/EXT_meshopt_compression
 */
class GLTFMeshoptCompression {

	constructor( parser ) {

		this.name = EXTENSIONS.EXT_MESHOPT_COMPRESSION;
		this.parser = parser;

	}

	loadBufferView( index ) {

		const json = this.parser.json;
		const bufferView = json.bufferViews[ index ];

		if ( bufferView.extensions && bufferView.extensions[ this.name ] ) {

			const extensionDef = bufferView.extensions[ this.name ];

			const buffer = this.parser.getDependency( 'buffer', extensionDef.buffer );
			const decoder = this.parser.options.meshoptDecoder;

			if ( ! decoder || ! decoder.supported ) {

				if ( json.extensionsRequired && json.extensionsRequired.indexOf( this.name ) >= 0 ) {

					throw new Error( 'THREE.GLTFLoader: setMeshoptDecoder must be called before loading compressed files' );

				} else {

					// Assumes that the extension is optional and that fallback buffer data is present
					return null;

				}

			}

			return Promise.all( [ buffer, decoder.ready ] ).then( function ( res ) {

				const byteOffset = extensionDef.byteOffset || 0;
				const byteLength = extensionDef.byteLength || 0;

				const count = extensionDef.count;
				const stride = extensionDef.byteStride;

				const result = new ArrayBuffer( count * stride );
				const source = new Uint8Array( res[ 0 ], byteOffset, byteLength );

				decoder.decodeGltfBuffer( new Uint8Array( result ), count, stride, source, extensionDef.mode, extensionDef.filter );
				return result;

			} );

		} else {

			return null;

		}

	}

}

/* BINARY EXTENSION */
const BINARY_EXTENSION_HEADER_MAGIC = 'glTF';
const BINARY_EXTENSION_HEADER_LENGTH = 12;
const BINARY_EXTENSION_CHUNK_TYPES = { JSON: 0x4E4F534A, BIN: 0x004E4942 };

class GLTFBinaryExtension {

	constructor( data ) {

		this.name = EXTENSIONS.KHR_BINARY_GLTF;
		this.content = null;
		this.body = null;

		const headerView = new DataView( data, 0, BINARY_EXTENSION_HEADER_LENGTH );

		this.header = {
			magic: LoaderUtils.decodeText( new Uint8Array( data.slice( 0, 4 ) ) ),
			version: headerView.getUint32( 4, true ),
			length: headerView.getUint32( 8, true )
		};

		if ( this.header.magic !== BINARY_EXTENSION_HEADER_MAGIC ) {

			throw new Error( 'THREE.GLTFLoader: Unsupported glTF-Binary header.' );

		} else if ( this.header.version < 2.0 ) {

			throw new Error( 'THREE.GLTFLoader: Legacy binary file detected.' );

		}

		const chunkContentsLength = this.header.length - BINARY_EXTENSION_HEADER_LENGTH;
		const chunkView = new DataView( data, BINARY_EXTENSION_HEADER_LENGTH );
		let chunkIndex = 0;

		while ( chunkIndex < chunkContentsLength ) {

			const chunkLength = chunkView.getUint32( chunkIndex, true );
			chunkIndex += 4;

			const chunkType = chunkView.getUint32( chunkIndex, true );
			chunkIndex += 4;

			if ( chunkType === BINARY_EXTENSION_CHUNK_TYPES.JSON ) {

				const contentArray = new Uint8Array( data, BINARY_EXTENSION_HEADER_LENGTH + chunkIndex, chunkLength );
				this.content = LoaderUtils.decodeText( contentArray );

			} else if ( chunkType === BINARY_EXTENSION_CHUNK_TYPES.BIN ) {

				const byteOffset = BINARY_EXTENSION_HEADER_LENGTH + chunkIndex;
				this.body = data.slice( byteOffset, byteOffset + chunkLength );

			}

			// Clients must ignore chunks with unknown types.

			chunkIndex += chunkLength;

		}

		if ( this.content === null ) {

			throw new Error( 'THREE.GLTFLoader: JSON content not found.' );

		}

	}

}

/**
 * DRACO Mesh Compression Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_draco_mesh_compression
 */
class GLTFDracoMeshCompressionExtension {

	constructor( json, dracoLoader ) {

		if ( ! dracoLoader ) {

			throw new Error( 'THREE.GLTFLoader: No DRACOLoader instance provided.' );

		}

		this.name = EXTENSIONS.KHR_DRACO_MESH_COMPRESSION;
		this.json = json;
		this.dracoLoader = dracoLoader;
		this.dracoLoader.preload();

	}

	decodePrimitive( primitive, parser ) {

		const json = this.json;
		const dracoLoader = this.dracoLoader;
		const bufferViewIndex = primitive.extensions[ this.name ].bufferView;
		const gltfAttributeMap = primitive.extensions[ this.name ].attributes;
		const threeAttributeMap = {};
		const attributeNormalizedMap = {};
		const attributeTypeMap = {};

		for ( const attributeName in gltfAttributeMap ) {

			const threeAttributeName = ATTRIBUTES[ attributeName ] || attributeName.toLowerCase();

			threeAttributeMap[ threeAttributeName ] = gltfAttributeMap[ attributeName ];

		}

		for ( const attributeName in primitive.attributes ) {

			const threeAttributeName = ATTRIBUTES[ attributeName ] || attributeName.toLowerCase();

			if ( gltfAttributeMap[ attributeName ] !== undefined ) {

				const accessorDef = json.accessors[ primitive.attributes[ attributeName ] ];
				const componentType = WEBGL_COMPONENT_TYPES[ accessorDef.componentType ];

				attributeTypeMap[ threeAttributeName ] = componentType;
				attributeNormalizedMap[ threeAttributeName ] = accessorDef.normalized === true;

			}

		}

		return parser.getDependency( 'bufferView', bufferViewIndex ).then( function ( bufferView ) {

			return new Promise( function ( resolve ) {

				dracoLoader.decodeDracoFile( bufferView, function ( geometry ) {

					for ( const attributeName in geometry.attributes ) {

						const attribute = geometry.attributes[ attributeName ];
						const normalized = attributeNormalizedMap[ attributeName ];

						if ( normalized !== undefined ) attribute.normalized = normalized;

					}

					resolve( geometry );

				}, threeAttributeMap, attributeTypeMap );

			} );

		} );

	}

}

/**
 * Texture Transform Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_transform
 */
class GLTFTextureTransformExtension {

	constructor() {

		this.name = EXTENSIONS.KHR_TEXTURE_TRANSFORM;

	}

	extendTexture( texture, transform ) {

		if ( transform.texCoord !== undefined ) {

			console.warn( 'THREE.GLTFLoader: Custom UV sets in "' + this.name + '" extension not yet supported.' );

		}

		if ( transform.offset === undefined && transform.rotation === undefined && transform.scale === undefined ) {

			// See https://github.com/mrdoob/three.js/issues/21819.
			return texture;

		}

		texture = texture.clone();

		if ( transform.offset !== undefined ) {

			texture.offset.fromArray( transform.offset );

		}

		if ( transform.rotation !== undefined ) {

			texture.rotation = transform.rotation;

		}

		if ( transform.scale !== undefined ) {

			texture.repeat.fromArray( transform.scale );

		}

		texture.needsUpdate = true;

		return texture;

	}

}

/**
 * Specular-Glossiness Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_pbrSpecularGlossiness
 */

/**
 * A sub class of StandardMaterial with some of the functionality
 * changed via the `onBeforeCompile` callback
 * @pailhead
 */
class GLTFMeshStandardSGMaterial extends MeshStandardMaterial {

	constructor( params ) {

		super();

		this.isGLTFSpecularGlossinessMaterial = true;

		//various chunks that need replacing
		const specularMapParsFragmentChunk = [
			'#ifdef USE_SPECULARMAP',
			'	uniform sampler2D specularMap;',
			'#endif'
		].join( '\n' );

		const glossinessMapParsFragmentChunk = [
			'#ifdef USE_GLOSSINESSMAP',
			'	uniform sampler2D glossinessMap;',
			'#endif'
		].join( '\n' );

		const specularMapFragmentChunk = [
			'vec3 specularFactor = specular;',
			'#ifdef USE_SPECULARMAP',
			'	vec4 texelSpecular = texture2D( specularMap, vUv );',
			'	texelSpecular = sRGBToLinear( texelSpecular );',
			'	// reads channel RGB, compatible with a glTF Specular-Glossiness (RGBA) texture',
			'	specularFactor *= texelSpecular.rgb;',
			'#endif'
		].join( '\n' );

		const glossinessMapFragmentChunk = [
			'float glossinessFactor = glossiness;',
			'#ifdef USE_GLOSSINESSMAP',
			'	vec4 texelGlossiness = texture2D( glossinessMap, vUv );',
			'	// reads channel A, compatible with a glTF Specular-Glossiness (RGBA) texture',
			'	glossinessFactor *= texelGlossiness.a;',
			'#endif'
		].join( '\n' );

		const lightPhysicalFragmentChunk = [
			'PhysicalMaterial material;',
			'material.diffuseColor = diffuseColor.rgb * ( 1. - max( specularFactor.r, max( specularFactor.g, specularFactor.b ) ) );',
			'vec3 dxy = max( abs( dFdx( geometryNormal ) ), abs( dFdy( geometryNormal ) ) );',
			'float geometryRoughness = max( max( dxy.x, dxy.y ), dxy.z );',
			'material.roughness = max( 1.0 - glossinessFactor, 0.0525 ); // 0.0525 corresponds to the base mip of a 256 cubemap.',
			'material.roughness += geometryRoughness;',
			'material.roughness = min( material.roughness, 1.0 );',
			'material.specularColor = specularFactor;',
		].join( '\n' );

		const uniforms = {
			specular: { value: new Color().setHex( 0xffffff ) },
			glossiness: { value: 1 },
			specularMap: { value: null },
			glossinessMap: { value: null }
		};

		this._extraUniforms = uniforms;

		this.onBeforeCompile = function ( shader ) {

			for ( const uniformName in uniforms ) {

				shader.uniforms[ uniformName ] = uniforms[ uniformName ];

			}

			shader.fragmentShader = shader.fragmentShader
				.replace( 'uniform float roughness;', 'uniform vec3 specular;' )
				.replace( 'uniform float metalness;', 'uniform float glossiness;' )
				.replace( '#include <roughnessmap_pars_fragment>', specularMapParsFragmentChunk )
				.replace( '#include <metalnessmap_pars_fragment>', glossinessMapParsFragmentChunk )
				.replace( '#include <roughnessmap_fragment>', specularMapFragmentChunk )
				.replace( '#include <metalnessmap_fragment>', glossinessMapFragmentChunk )
				.replace( '#include <lights_physical_fragment>', lightPhysicalFragmentChunk );

		};

		Object.defineProperties( this, {

			specular: {
				get: function () {

					return uniforms.specular.value;

				},
				set: function ( v ) {

					uniforms.specular.value = v;

				}
			},

			specularMap: {
				get: function () {

					return uniforms.specularMap.value;

				},
				set: function ( v ) {

					uniforms.specularMap.value = v;

					if ( v ) {

						this.defines.USE_SPECULARMAP = ''; // USE_UV is set by the renderer for specular maps

					} else {

						delete this.defines.USE_SPECULARMAP;

					}

				}
			},

			glossiness: {
				get: function () {

					return uniforms.glossiness.value;

				},
				set: function ( v ) {

					uniforms.glossiness.value = v;

				}
			},

			glossinessMap: {
				get: function () {

					return uniforms.glossinessMap.value;

				},
				set: function ( v ) {

					uniforms.glossinessMap.value = v;

					if ( v ) {

						this.defines.USE_GLOSSINESSMAP = '';
						this.defines.USE_UV = '';

					} else {

						delete this.defines.USE_GLOSSINESSMAP;
						delete this.defines.USE_UV;

					}

				}
			}

		} );

		delete this.metalness;
		delete this.roughness;
		delete this.metalnessMap;
		delete this.roughnessMap;

		this.setValues( params );

	}

	copy( source ) {

		super.copy( source );

		this.specularMap = source.specularMap;
		this.specular.copy( source.specular );
		this.glossinessMap = source.glossinessMap;
		this.glossiness = source.glossiness;
		delete this.metalness;
		delete this.roughness;
		delete this.metalnessMap;
		delete this.roughnessMap;
		return this;

	}

}


class GLTFMaterialsPbrSpecularGlossinessExtension {

	constructor() {

		this.name = EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS;

		this.specularGlossinessParams = [
			'color',
			'map',
			'lightMap',
			'lightMapIntensity',
			'aoMap',
			'aoMapIntensity',
			'emissive',
			'emissiveIntensity',
			'emissiveMap',
			'bumpMap',
			'bumpScale',
			'normalMap',
			'normalMapType',
			'displacementMap',
			'displacementScale',
			'displacementBias',
			'specularMap',
			'specular',
			'glossinessMap',
			'glossiness',
			'alphaMap',
			'envMap',
			'envMapIntensity',
			'refractionRatio',
		];

	}

	getMaterialType() {

		return GLTFMeshStandardSGMaterial;

	}

	extendParams( materialParams, materialDef, parser ) {

		const pbrSpecularGlossiness = materialDef.extensions[ this.name ];

		materialParams.color = new Color( 1.0, 1.0, 1.0 );
		materialParams.opacity = 1.0;

		const pending = [];

		if ( Array.isArray( pbrSpecularGlossiness.diffuseFactor ) ) {

			const array = pbrSpecularGlossiness.diffuseFactor;

			materialParams.color.fromArray( array );
			materialParams.opacity = array[ 3 ];

		}

		if ( pbrSpecularGlossiness.diffuseTexture !== undefined ) {

			pending.push( parser.assignTexture( materialParams, 'map', pbrSpecularGlossiness.diffuseTexture ) );

		}

		materialParams.emissive = new Color( 0.0, 0.0, 0.0 );
		materialParams.glossiness = pbrSpecularGlossiness.glossinessFactor !== undefined ? pbrSpecularGlossiness.glossinessFactor : 1.0;
		materialParams.specular = new Color( 1.0, 1.0, 1.0 );

		if ( Array.isArray( pbrSpecularGlossiness.specularFactor ) ) {

			materialParams.specular.fromArray( pbrSpecularGlossiness.specularFactor );

		}

		if ( pbrSpecularGlossiness.specularGlossinessTexture !== undefined ) {

			const specGlossMapDef = pbrSpecularGlossiness.specularGlossinessTexture;
			pending.push( parser.assignTexture( materialParams, 'glossinessMap', specGlossMapDef ) );
			pending.push( parser.assignTexture( materialParams, 'specularMap', specGlossMapDef ) );

		}

		return Promise.all( pending );

	}

	createMaterial( materialParams ) {

		const material = new GLTFMeshStandardSGMaterial( materialParams );
		material.fog = true;

		material.color = materialParams.color;

		material.map = materialParams.map === undefined ? null : materialParams.map;

		material.lightMap = null;
		material.lightMapIntensity = 1.0;

		material.aoMap = materialParams.aoMap === undefined ? null : materialParams.aoMap;
		material.aoMapIntensity = 1.0;

		material.emissive = materialParams.emissive;
		material.emissiveIntensity = 1.0;
		material.emissiveMap = materialParams.emissiveMap === undefined ? null : materialParams.emissiveMap;

		material.bumpMap = materialParams.bumpMap === undefined ? null : materialParams.bumpMap;
		material.bumpScale = 1;

		material.normalMap = materialParams.normalMap === undefined ? null : materialParams.normalMap;
		material.normalMapType = TangentSpaceNormalMap;

		if ( materialParams.normalScale ) material.normalScale = materialParams.normalScale;

		material.displacementMap = null;
		material.displacementScale = 1;
		material.displacementBias = 0;

		material.specularMap = materialParams.specularMap === undefined ? null : materialParams.specularMap;
		material.specular = materialParams.specular;

		material.glossinessMap = materialParams.glossinessMap === undefined ? null : materialParams.glossinessMap;
		material.glossiness = materialParams.glossiness;

		material.alphaMap = null;

		material.envMap = materialParams.envMap === undefined ? null : materialParams.envMap;
		material.envMapIntensity = 1.0;

		material.refractionRatio = 0.98;

		return material;

	}

}

/**
 * Mesh Quantization Extension
 *
 * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_mesh_quantization
 */
class GLTFMeshQuantizationExtension {

	constructor() {

		this.name = EXTENSIONS.KHR_MESH_QUANTIZATION;

	}

}

/*********************************/
/********** INTERPOLATION ********/
/*********************************/

// Spline Interpolation
// Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#appendix-c-spline-interpolation
class GLTFCubicSplineInterpolant extends Interpolant {

	constructor( parameterPositions, sampleValues, sampleSize, resultBuffer ) {

		super( parameterPositions, sampleValues, sampleSize, resultBuffer );

	}

	copySampleValue_( index ) {

		// Copies a sample value to the result buffer. See description of glTF
		// CUBICSPLINE values layout in interpolate_() function below.

		const result = this.resultBuffer,
			values = this.sampleValues,
			valueSize = this.valueSize,
			offset = index * valueSize * 3 + valueSize;

		for ( let i = 0; i !== valueSize; i ++ ) {

			result[ i ] = values[ offset + i ];

		}

		return result;

	}

}

GLTFCubicSplineInterpolant.prototype.beforeStart_ = GLTFCubicSplineInterpolant.prototype.copySampleValue_;

GLTFCubicSplineInterpolant.prototype.afterEnd_ = GLTFCubicSplineInterpolant.prototype.copySampleValue_;

GLTFCubicSplineInterpolant.prototype.interpolate_ = function ( i1, t0, t, t1 ) {

	const result = this.resultBuffer;
	const values = this.sampleValues;
	const stride = this.valueSize;

	const stride2 = stride * 2;
	const stride3 = stride * 3;

	const td = t1 - t0;

	const p = ( t - t0 ) / td;
	const pp = p * p;
	const ppp = pp * p;

	const offset1 = i1 * stride3;
	const offset0 = offset1 - stride3;

	const s2 = - 2 * ppp + 3 * pp;
	const s3 = ppp - pp;
	const s0 = 1 - s2;
	const s1 = s3 - pp + p;

	// Layout of keyframe output values for CUBICSPLINE animations:
	//   [ inTangent_1, splineVertex_1, outTangent_1, inTangent_2, splineVertex_2, ... ]
	for ( let i = 0; i !== stride; i ++ ) {

		const p0 = values[ offset0 + i + stride ]; // splineVertex_k
		const m0 = values[ offset0 + i + stride2 ] * td; // outTangent_k * (t_k+1 - t_k)
		const p1 = values[ offset1 + i + stride ]; // splineVertex_k+1
		const m1 = values[ offset1 + i ] * td; // inTangent_k+1 * (t_k+1 - t_k)

		result[ i ] = s0 * p0 + s1 * m0 + s2 * p1 + s3 * m1;

	}

	return result;

};

const _q = new Quaternion();

class GLTFCubicSplineQuaternionInterpolant extends GLTFCubicSplineInterpolant {

	interpolate_( i1, t0, t, t1 ) {

		const result = super.interpolate_( i1, t0, t, t1 );

		_q.fromArray( result ).normalize().toArray( result );

		return result;

	}

}


/*********************************/
/********** INTERNALS ************/
/*********************************/

/* CONSTANTS */

const WEBGL_CONSTANTS = {
	FLOAT: 5126,
	//FLOAT_MAT2: 35674,
	FLOAT_MAT3: 35675,
	FLOAT_MAT4: 35676,
	FLOAT_VEC2: 35664,
	FLOAT_VEC3: 35665,
	FLOAT_VEC4: 35666,
	LINEAR: 9729,
	REPEAT: 10497,
	SAMPLER_2D: 35678,
	POINTS: 0,
	LINES: 1,
	LINE_LOOP: 2,
	LINE_STRIP: 3,
	TRIANGLES: 4,
	TRIANGLE_STRIP: 5,
	TRIANGLE_FAN: 6,
	UNSIGNED_BYTE: 5121,
	UNSIGNED_SHORT: 5123
};

const WEBGL_COMPONENT_TYPES = {
	5120: Int8Array,
	5121: Uint8Array,
	5122: Int16Array,
	5123: Uint16Array,
	5125: Uint32Array,
	5126: Float32Array
};

const WEBGL_FILTERS = {
	9728: NearestFilter,
	9729: LinearFilter,
	9984: NearestMipmapNearestFilter,
	9985: LinearMipmapNearestFilter,
	9986: NearestMipmapLinearFilter,
	9987: LinearMipmapLinearFilter
};

const WEBGL_WRAPPINGS = {
	33071: ClampToEdgeWrapping,
	33648: MirroredRepeatWrapping,
	10497: RepeatWrapping
};

const WEBGL_TYPE_SIZES = {
	'SCALAR': 1,
	'VEC2': 2,
	'VEC3': 3,
	'VEC4': 4,
	'MAT2': 4,
	'MAT3': 9,
	'MAT4': 16
};

const ATTRIBUTES = {
	POSITION: 'position',
	NORMAL: 'normal',
	TANGENT: 'tangent',
	TEXCOORD_0: 'uv',
	TEXCOORD_1: 'uv2',
	COLOR_0: 'color',
	WEIGHTS_0: 'skinWeight',
	JOINTS_0: 'skinIndex',
};

const PATH_PROPERTIES = {
	scale: 'scale',
	translation: 'position',
	rotation: 'quaternion',
	weights: 'morphTargetInfluences'
};

const INTERPOLATION = {
	CUBICSPLINE: undefined, // We use a custom interpolant (GLTFCubicSplineInterpolation) for CUBICSPLINE tracks. Each
		                        // keyframe track will be initialized with a default interpolation type, then modified.
	LINEAR: InterpolateLinear,
	STEP: InterpolateDiscrete
};

const ALPHA_MODES = {
	OPAQUE: 'OPAQUE',
	MASK: 'MASK',
	BLEND: 'BLEND'
};

/* UTILITY FUNCTIONS */

function resolveURL( url, path ) {

	// Invalid URL
	if ( typeof url !== 'string' || url === '' ) return '';

	// Host Relative URL
	if ( /^https?:\/\//i.test( path ) && /^\//.test( url ) ) {

		path = path.replace( /(^https?:\/\/[^\/]+).*/i, '$1' );

	}

	// Absolute URL http://,https://,//
	if ( /^(https?:)?\/\//i.test( url ) ) return url;

	// Data URI
	if ( /^data:.*,.*$/i.test( url ) ) return url;

	// Blob URL
	if ( /^blob:.*$/i.test( url ) ) return url;

	// Relative URL
	return path + url;

}

/**
 * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#default-material
 */
function createDefaultMaterial( cache ) {

	if ( cache[ 'DefaultMaterial' ] === undefined ) {

		cache[ 'DefaultMaterial' ] = new MeshStandardMaterial( {
			color: 0xFFFFFF,
			emissive: 0x000000,
			metalness: 1,
			roughness: 1,
			transparent: false,
			depthTest: true,
			side: FrontSide
		} );

	}

	return cache[ 'DefaultMaterial' ];

}

function addUnknownExtensionsToUserData( knownExtensions, object, objectDef ) {

	// Add unknown glTF extensions to an object's userData.

	for ( const name in objectDef.extensions ) {

		if ( knownExtensions[ name ] === undefined ) {

			object.userData.gltfExtensions = object.userData.gltfExtensions || {};
			object.userData.gltfExtensions[ name ] = objectDef.extensions[ name ];

		}

	}

}

/**
 * @param {Object3D|Material|BufferGeometry} object
 * @param {GLTF.definition} gltfDef
 */
function assignExtrasToUserData( object, gltfDef ) {

	if ( gltfDef.extras !== undefined ) {

		if ( typeof gltfDef.extras === 'object' ) {

			Object.assign( object.userData, gltfDef.extras );

		} else {

			console.warn( 'THREE.GLTFLoader: Ignoring primitive type .extras, ' + gltfDef.extras );

		}

	}

}

/**
 * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#morph-targets
 *
 * @param {BufferGeometry} geometry
 * @param {Array<GLTF.Target>} targets
 * @param {GLTFParser} parser
 * @return {Promise<BufferGeometry>}
 */
function addMorphTargets( geometry, targets, parser ) {

	let hasMorphPosition = false;
	let hasMorphNormal = false;

	for ( let i = 0, il = targets.length; i < il; i ++ ) {

		const target = targets[ i ];

		if ( target.POSITION !== undefined ) hasMorphPosition = true;
		if ( target.NORMAL !== undefined ) hasMorphNormal = true;

		if ( hasMorphPosition && hasMorphNormal ) break;

	}

	if ( ! hasMorphPosition && ! hasMorphNormal ) return Promise.resolve( geometry );

	const pendingPositionAccessors = [];
	const pendingNormalAccessors = [];

	for ( let i = 0, il = targets.length; i < il; i ++ ) {

		const target = targets[ i ];

		if ( hasMorphPosition ) {

			const pendingAccessor = target.POSITION !== undefined
				? parser.getDependency( 'accessor', target.POSITION )
				: geometry.attributes.position;

			pendingPositionAccessors.push( pendingAccessor );

		}

		if ( hasMorphNormal ) {

			const pendingAccessor = target.NORMAL !== undefined
				? parser.getDependency( 'accessor', target.NORMAL )
				: geometry.attributes.normal;

			pendingNormalAccessors.push( pendingAccessor );

		}

	}

	return Promise.all( [
		Promise.all( pendingPositionAccessors ),
		Promise.all( pendingNormalAccessors )
	] ).then( function ( accessors ) {

		const morphPositions = accessors[ 0 ];
		const morphNormals = accessors[ 1 ];

		if ( hasMorphPosition ) geometry.morphAttributes.position = morphPositions;
		if ( hasMorphNormal ) geometry.morphAttributes.normal = morphNormals;
		geometry.morphTargetsRelative = true;

		return geometry;

	} );

}

/**
 * @param {Mesh} mesh
 * @param {GLTF.Mesh} meshDef
 */
function updateMorphTargets( mesh, meshDef ) {

	mesh.updateMorphTargets();

	if ( meshDef.weights !== undefined ) {

		for ( let i = 0, il = meshDef.weights.length; i < il; i ++ ) {

			mesh.morphTargetInfluences[ i ] = meshDef.weights[ i ];

		}

	}

	// .extras has user-defined data, so check that .extras.targetNames is an array.
	if ( meshDef.extras && Array.isArray( meshDef.extras.targetNames ) ) {

		const targetNames = meshDef.extras.targetNames;

		if ( mesh.morphTargetInfluences.length === targetNames.length ) {

			mesh.morphTargetDictionary = {};

			for ( let i = 0, il = targetNames.length; i < il; i ++ ) {

				mesh.morphTargetDictionary[ targetNames[ i ] ] = i;

			}

		} else {

			console.warn( 'THREE.GLTFLoader: Invalid extras.targetNames length. Ignoring names.' );

		}

	}

}

function createPrimitiveKey( primitiveDef ) {

	const dracoExtension = primitiveDef.extensions && primitiveDef.extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ];
	let geometryKey;

	if ( dracoExtension ) {

		geometryKey = 'draco:' + dracoExtension.bufferView
				+ ':' + dracoExtension.indices
				+ ':' + createAttributesKey( dracoExtension.attributes );

	} else {

		geometryKey = primitiveDef.indices + ':' + createAttributesKey( primitiveDef.attributes ) + ':' + primitiveDef.mode;

	}

	return geometryKey;

}

function createAttributesKey( attributes ) {

	let attributesKey = '';

	const keys = Object.keys( attributes ).sort();

	for ( let i = 0, il = keys.length; i < il; i ++ ) {

		attributesKey += keys[ i ] + ':' + attributes[ keys[ i ] ] + ';';

	}

	return attributesKey;

}

function getNormalizedComponentScale( constructor ) {

	// Reference:
	// https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_mesh_quantization#encoding-quantized-data

	switch ( constructor ) {

		case Int8Array:
			return 1 / 127;

		case Uint8Array:
			return 1 / 255;

		case Int16Array:
			return 1 / 32767;

		case Uint16Array:
			return 1 / 65535;

		default:
			throw new Error( 'THREE.GLTFLoader: Unsupported normalized accessor component type.' );

	}

}

/* GLTF PARSER */

class GLTFParser {

	constructor( json = {}, options = {} ) {

		this.json = json;
		this.extensions = {};
		this.plugins = {};
		this.options = options;

		// loader object cache
		this.cache = new GLTFRegistry();

		// associations between Three.js objects and glTF elements
		this.associations = new Map();

		// BufferGeometry caching
		this.primitiveCache = {};

		// Object3D instance caches
		this.meshCache = { refs: {}, uses: {} };
		this.cameraCache = { refs: {}, uses: {} };
		this.lightCache = { refs: {}, uses: {} };

		this.textureCache = {};

		// Track node names, to ensure no duplicates
		this.nodeNamesUsed = {};

		// Use an ImageBitmapLoader if imageBitmaps are supported. Moves much of the
		// expensive work of uploading a texture to the GPU off the main thread.
		if ( typeof createImageBitmap !== 'undefined' && /Firefox/.test( navigator.userAgent ) === false ) {

			this.textureLoader = new ImageBitmapLoader( this.options.manager );

		} else {

			this.textureLoader = new TextureLoader( this.options.manager );

		}

		this.textureLoader.setCrossOrigin( this.options.crossOrigin );
		this.textureLoader.setRequestHeader( this.options.requestHeader );

		this.fileLoader = new FileLoader( this.options.manager );
		this.fileLoader.setResponseType( 'arraybuffer' );

		if ( this.options.crossOrigin === 'use-credentials' ) {

			this.fileLoader.setWithCredentials( true );

		}

	}

	setExtensions( extensions ) {

		this.extensions = extensions;

	}

	setPlugins( plugins ) {

		this.plugins = plugins;

	}

	parse( onLoad, onError ) {

		const parser = this;
		const json = this.json;
		const extensions = this.extensions;

		// Clear the loader cache
		this.cache.removeAll();

		// Mark the special nodes/meshes in json for efficient parse
		this._invokeAll( function ( ext ) {

			return ext._markDefs && ext._markDefs();

		} );

		Promise.all( this._invokeAll( function ( ext ) {

			return ext.beforeRoot && ext.beforeRoot();

		} ) ).then( function () {

			return Promise.all( [

				parser.getDependencies( 'scene' ),
				parser.getDependencies( 'animation' ),
				parser.getDependencies( 'camera' ),

			] );

		} ).then( function ( dependencies ) {

			const result = {
				scene: dependencies[ 0 ][ json.scene || 0 ],
				scenes: dependencies[ 0 ],
				animations: dependencies[ 1 ],
				cameras: dependencies[ 2 ],
				asset: json.asset,
				parser: parser,
				userData: {}
			};

			addUnknownExtensionsToUserData( extensions, result, json );

			assignExtrasToUserData( result, json );

			Promise.all( parser._invokeAll( function ( ext ) {

				return ext.afterRoot && ext.afterRoot( result );

			} ) ).then( function () {

				onLoad( result );

			} );

		} ).catch( onError );

	}

	/**
	 * Marks the special nodes/meshes in json for efficient parse.
	 */
	_markDefs() {

		const nodeDefs = this.json.nodes || [];
		const skinDefs = this.json.skins || [];
		const meshDefs = this.json.meshes || [];

		// Nothing in the node definition indicates whether it is a Bone or an
		// Object3D. Use the skins' joint references to mark bones.
		for ( let skinIndex = 0, skinLength = skinDefs.length; skinIndex < skinLength; skinIndex ++ ) {

			const joints = skinDefs[ skinIndex ].joints;

			for ( let i = 0, il = joints.length; i < il; i ++ ) {

				nodeDefs[ joints[ i ] ].isBone = true;

			}

		}

		// Iterate over all nodes, marking references to shared resources,
		// as well as skeleton joints.
		for ( let nodeIndex = 0, nodeLength = nodeDefs.length; nodeIndex < nodeLength; nodeIndex ++ ) {

			const nodeDef = nodeDefs[ nodeIndex ];

			if ( nodeDef.mesh !== undefined ) {

				this._addNodeRef( this.meshCache, nodeDef.mesh );

				// Nothing in the mesh definition indicates whether it is
				// a SkinnedMesh or Mesh. Use the node's mesh reference
				// to mark SkinnedMesh if node has skin.
				if ( nodeDef.skin !== undefined ) {

					meshDefs[ nodeDef.mesh ].isSkinnedMesh = true;

				}

			}

			if ( nodeDef.camera !== undefined ) {

				this._addNodeRef( this.cameraCache, nodeDef.camera );

			}

		}

	}

	/**
	 * Counts references to shared node / Object3D resources. These resources
	 * can be reused, or "instantiated", at multiple nodes in the scene
	 * hierarchy. Mesh, Camera, and Light instances are instantiated and must
	 * be marked. Non-scenegraph resources (like Materials, Geometries, and
	 * Textures) can be reused directly and are not marked here.
	 *
	 * Example: CesiumMilkTruck sample model reuses "Wheel" meshes.
	 */
	_addNodeRef( cache, index ) {

		if ( index === undefined ) return;

		if ( cache.refs[ index ] === undefined ) {

			cache.refs[ index ] = cache.uses[ index ] = 0;

		}

		cache.refs[ index ] ++;

	}

	/** Returns a reference to a shared resource, cloning it if necessary. */
	_getNodeRef( cache, index, object ) {

		if ( cache.refs[ index ] <= 1 ) return object;

		const ref = object.clone();

		// Propagates mappings to the cloned object, prevents mappings on the
		// original object from being lost.
		const updateMappings = ( original, clone ) => {

			const mappings = this.associations.get( original );
			if ( mappings != null ) {

				this.associations.set( clone, mappings );

			}

			for ( const [ i, child ] of original.children.entries() ) {

				updateMappings( child, clone.children[ i ] );

			}

		};

		updateMappings( object, ref );

		ref.name += '_instance_' + ( cache.uses[ index ] ++ );

		return ref;

	}

	_invokeOne( func ) {

		const extensions = Object.values( this.plugins );
		extensions.push( this );

		for ( let i = 0; i < extensions.length; i ++ ) {

			const result = func( extensions[ i ] );

			if ( result ) return result;

		}

		return null;

	}

	_invokeAll( func ) {

		const extensions = Object.values( this.plugins );
		extensions.unshift( this );

		const pending = [];

		for ( let i = 0; i < extensions.length; i ++ ) {

			const result = func( extensions[ i ] );

			if ( result ) pending.push( result );

		}

		return pending;

	}

	/**
	 * Requests the specified dependency asynchronously, with caching.
	 * @param {string} type
	 * @param {number} index
	 * @return {Promise<Object3D|Material|THREE.Texture|AnimationClip|ArrayBuffer|Object>}
	 */
	getDependency( type, index ) {

		const cacheKey = type + ':' + index;
		let dependency = this.cache.get( cacheKey );

		if ( ! dependency ) {

			switch ( type ) {

				case 'scene':
					dependency = this.loadScene( index );
					break;

				case 'node':
					dependency = this.loadNode( index );
					break;

				case 'mesh':
					dependency = this._invokeOne( function ( ext ) {

						return ext.loadMesh && ext.loadMesh( index );

					} );
					break;

				case 'accessor':
					dependency = this.loadAccessor( index );
					break;

				case 'bufferView':
					dependency = this._invokeOne( function ( ext ) {

						return ext.loadBufferView && ext.loadBufferView( index );

					} );
					break;

				case 'buffer':
					dependency = this.loadBuffer( index );
					break;

				case 'material':
					dependency = this._invokeOne( function ( ext ) {

						return ext.loadMaterial && ext.loadMaterial( index );

					} );
					break;

				case 'texture':
					dependency = this._invokeOne( function ( ext ) {

						return ext.loadTexture && ext.loadTexture( index );

					} );
					break;

				case 'skin':
					dependency = this.loadSkin( index );
					break;

				case 'animation':
					dependency = this.loadAnimation( index );
					break;

				case 'camera':
					dependency = this.loadCamera( index );
					break;

				default:
					throw new Error( 'Unknown type: ' + type );

			}

			this.cache.add( cacheKey, dependency );

		}

		return dependency;

	}

	/**
	 * Requests all dependencies of the specified type asynchronously, with caching.
	 * @param {string} type
	 * @return {Promise<Array<Object>>}
	 */
	getDependencies( type ) {

		let dependencies = this.cache.get( type );

		if ( ! dependencies ) {

			const parser = this;
			const defs = this.json[ type + ( type === 'mesh' ? 'es' : 's' ) ] || [];

			dependencies = Promise.all( defs.map( function ( def, index ) {

				return parser.getDependency( type, index );

			} ) );

			this.cache.add( type, dependencies );

		}

		return dependencies;

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#buffers-and-buffer-views
	 * @param {number} bufferIndex
	 * @return {Promise<ArrayBuffer>}
	 */
	loadBuffer( bufferIndex ) {

		const bufferDef = this.json.buffers[ bufferIndex ];
		const loader = this.fileLoader;

		if ( bufferDef.type && bufferDef.type !== 'arraybuffer' ) {

			throw new Error( 'THREE.GLTFLoader: ' + bufferDef.type + ' buffer type is not supported.' );

		}

		// If present, GLB container is required to be the first buffer.
		if ( bufferDef.uri === undefined && bufferIndex === 0 ) {

			return Promise.resolve( this.extensions[ EXTENSIONS.KHR_BINARY_GLTF ].body );

		}

		const options = this.options;

		return new Promise( function ( resolve, reject ) {

			loader.load( resolveURL( bufferDef.uri, options.path ), resolve, undefined, function () {

				reject( new Error( 'THREE.GLTFLoader: Failed to load buffer "' + bufferDef.uri + '".' ) );

			} );

		} );

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#buffers-and-buffer-views
	 * @param {number} bufferViewIndex
	 * @return {Promise<ArrayBuffer>}
	 */
	loadBufferView( bufferViewIndex ) {

		const bufferViewDef = this.json.bufferViews[ bufferViewIndex ];

		return this.getDependency( 'buffer', bufferViewDef.buffer ).then( function ( buffer ) {

			const byteLength = bufferViewDef.byteLength || 0;
			const byteOffset = bufferViewDef.byteOffset || 0;
			return buffer.slice( byteOffset, byteOffset + byteLength );

		} );

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#accessors
	 * @param {number} accessorIndex
	 * @return {Promise<BufferAttribute|InterleavedBufferAttribute>}
	 */
	loadAccessor( accessorIndex ) {

		const parser = this;
		const json = this.json;

		const accessorDef = this.json.accessors[ accessorIndex ];

		if ( accessorDef.bufferView === undefined && accessorDef.sparse === undefined ) {

			// Ignore empty accessors, which may be used to declare runtime
			// information about attributes coming from another source (e.g. Draco
			// compression extension).
			return Promise.resolve( null );

		}

		const pendingBufferViews = [];

		if ( accessorDef.bufferView !== undefined ) {

			pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.bufferView ) );

		} else {

			pendingBufferViews.push( null );

		}

		if ( accessorDef.sparse !== undefined ) {

			pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.sparse.indices.bufferView ) );
			pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.sparse.values.bufferView ) );

		}

		return Promise.all( pendingBufferViews ).then( function ( bufferViews ) {

			const bufferView = bufferViews[ 0 ];

			const itemSize = WEBGL_TYPE_SIZES[ accessorDef.type ];
			const TypedArray = WEBGL_COMPONENT_TYPES[ accessorDef.componentType ];

			// For VEC3: itemSize is 3, elementBytes is 4, itemBytes is 12.
			const elementBytes = TypedArray.BYTES_PER_ELEMENT;
			const itemBytes = elementBytes * itemSize;
			const byteOffset = accessorDef.byteOffset || 0;
			const byteStride = accessorDef.bufferView !== undefined ? json.bufferViews[ accessorDef.bufferView ].byteStride : undefined;
			const normalized = accessorDef.normalized === true;
			let array, bufferAttribute;

			// The buffer is not interleaved if the stride is the item size in bytes.
			if ( byteStride && byteStride !== itemBytes ) {

				// Each "slice" of the buffer, as defined by 'count' elements of 'byteStride' bytes, gets its own InterleavedBuffer
				// This makes sure that IBA.count reflects accessor.count properly
				const ibSlice = Math.floor( byteOffset / byteStride );
				const ibCacheKey = 'InterleavedBuffer:' + accessorDef.bufferView + ':' + accessorDef.componentType + ':' + ibSlice + ':' + accessorDef.count;
				let ib = parser.cache.get( ibCacheKey );

				if ( ! ib ) {

					array = new TypedArray( bufferView, ibSlice * byteStride, accessorDef.count * byteStride / elementBytes );

					// Integer parameters to IB/IBA are in array elements, not bytes.
					ib = new InterleavedBuffer( array, byteStride / elementBytes );

					parser.cache.add( ibCacheKey, ib );

				}

				bufferAttribute = new InterleavedBufferAttribute( ib, itemSize, ( byteOffset % byteStride ) / elementBytes, normalized );

			} else {

				if ( bufferView === null ) {

					array = new TypedArray( accessorDef.count * itemSize );

				} else {

					array = new TypedArray( bufferView, byteOffset, accessorDef.count * itemSize );

				}

				bufferAttribute = new BufferAttribute( array, itemSize, normalized );

			}

			// https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#sparse-accessors
			if ( accessorDef.sparse !== undefined ) {

				const itemSizeIndices = WEBGL_TYPE_SIZES.SCALAR;
				const TypedArrayIndices = WEBGL_COMPONENT_TYPES[ accessorDef.sparse.indices.componentType ];

				const byteOffsetIndices = accessorDef.sparse.indices.byteOffset || 0;
				const byteOffsetValues = accessorDef.sparse.values.byteOffset || 0;

				const sparseIndices = new TypedArrayIndices( bufferViews[ 1 ], byteOffsetIndices, accessorDef.sparse.count * itemSizeIndices );
				const sparseValues = new TypedArray( bufferViews[ 2 ], byteOffsetValues, accessorDef.sparse.count * itemSize );

				if ( bufferView !== null ) {

					// Avoid modifying the original ArrayBuffer, if the bufferView wasn't initialized with zeroes.
					bufferAttribute = new BufferAttribute( bufferAttribute.array.slice(), bufferAttribute.itemSize, bufferAttribute.normalized );

				}

				for ( let i = 0, il = sparseIndices.length; i < il; i ++ ) {

					const index = sparseIndices[ i ];

					bufferAttribute.setX( index, sparseValues[ i * itemSize ] );
					if ( itemSize >= 2 ) bufferAttribute.setY( index, sparseValues[ i * itemSize + 1 ] );
					if ( itemSize >= 3 ) bufferAttribute.setZ( index, sparseValues[ i * itemSize + 2 ] );
					if ( itemSize >= 4 ) bufferAttribute.setW( index, sparseValues[ i * itemSize + 3 ] );
					if ( itemSize >= 5 ) throw new Error( 'THREE.GLTFLoader: Unsupported itemSize in sparse BufferAttribute.' );

				}

			}

			return bufferAttribute;

		} );

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#textures
	 * @param {number} textureIndex
	 * @return {Promise<THREE.Texture>}
	 */
	loadTexture( textureIndex ) {

		const json = this.json;
		const options = this.options;
		const textureDef = json.textures[ textureIndex ];
		const source = json.images[ textureDef.source ];

		let loader = this.textureLoader;

		if ( source.uri ) {

			const handler = options.manager.getHandler( source.uri );
			if ( handler !== null ) loader = handler;

		}

		return this.loadTextureImage( textureIndex, source, loader );

	}

	loadTextureImage( textureIndex, source, loader ) {

		const parser = this;
		const json = this.json;
		const options = this.options;

		const textureDef = json.textures[ textureIndex ];

		const cacheKey = ( source.uri || source.bufferView ) + ':' + textureDef.sampler;

		if ( this.textureCache[ cacheKey ] ) {

			// See https://github.com/mrdoob/three.js/issues/21559.
			return this.textureCache[ cacheKey ];

		}

		const URL = self.URL || self.webkitURL;

		let sourceURI = source.uri || '';
		let isObjectURL = false;

		if ( source.bufferView !== undefined ) {

			// Load binary image data from bufferView, if provided.

			sourceURI = parser.getDependency( 'bufferView', source.bufferView ).then( function ( bufferView ) {

				isObjectURL = true;
				const blob = new Blob( [ bufferView ], { type: source.mimeType } );
				sourceURI = URL.createObjectURL( blob );
				return sourceURI;

			} );

		} else if ( source.uri === undefined ) {

			throw new Error( 'THREE.GLTFLoader: Image ' + textureIndex + ' is missing URI and bufferView' );

		}

		const promise = Promise.resolve( sourceURI ).then( function ( sourceURI ) {

			return new Promise( function ( resolve, reject ) {

				let onLoad = resolve;

				if ( loader.isImageBitmapLoader === true ) {

					onLoad = function ( imageBitmap ) {

						const texture = new Texture( imageBitmap );
						texture.needsUpdate = true;

						resolve( texture );

					};

				}

				loader.load( resolveURL( sourceURI, options.path ), onLoad, undefined, reject );

			} );

		} ).then( function ( texture ) {

			// Clean up resources and configure Texture.

			if ( isObjectURL === true ) {

				URL.revokeObjectURL( sourceURI );

			}

			texture.flipY = false;

			if ( textureDef.name ) texture.name = textureDef.name;

			const samplers = json.samplers || {};
			const sampler = samplers[ textureDef.sampler ] || {};

			texture.magFilter = WEBGL_FILTERS[ sampler.magFilter ] || LinearFilter;
			texture.minFilter = WEBGL_FILTERS[ sampler.minFilter ] || LinearMipmapLinearFilter;
			texture.wrapS = WEBGL_WRAPPINGS[ sampler.wrapS ] || RepeatWrapping;
			texture.wrapT = WEBGL_WRAPPINGS[ sampler.wrapT ] || RepeatWrapping;

			parser.associations.set( texture, { textures: textureIndex } );

			return texture;

		} ).catch( function () {

			console.error( 'THREE.GLTFLoader: Couldn\'t load texture', sourceURI );
			return null;

		} );

		this.textureCache[ cacheKey ] = promise;

		return promise;

	}

	/**
	 * Asynchronously assigns a texture to the given material parameters.
	 * @param {Object} materialParams
	 * @param {string} mapName
	 * @param {Object} mapDef
	 * @return {Promise<Texture>}
	 */
	assignTexture( materialParams, mapName, mapDef ) {

		const parser = this;

		return this.getDependency( 'texture', mapDef.index ).then( function ( texture ) {

			// Materials sample aoMap from UV set 1 and other maps from UV set 0 - this can't be configured
			// However, we will copy UV set 0 to UV set 1 on demand for aoMap
			if ( mapDef.texCoord !== undefined && mapDef.texCoord != 0 && ! ( mapName === 'aoMap' && mapDef.texCoord == 1 ) ) {

				console.warn( 'THREE.GLTFLoader: Custom UV set ' + mapDef.texCoord + ' for texture ' + mapName + ' not yet supported.' );

			}

			if ( parser.extensions[ EXTENSIONS.KHR_TEXTURE_TRANSFORM ] ) {

				const transform = mapDef.extensions !== undefined ? mapDef.extensions[ EXTENSIONS.KHR_TEXTURE_TRANSFORM ] : undefined;

				if ( transform ) {

					const gltfReference = parser.associations.get( texture );
					texture = parser.extensions[ EXTENSIONS.KHR_TEXTURE_TRANSFORM ].extendTexture( texture, transform );
					parser.associations.set( texture, gltfReference );

				}

			}

			materialParams[ mapName ] = texture;

			return texture;

		} );

	}

	/**
	 * Assigns final material to a Mesh, Line, or Points instance. The instance
	 * already has a material (generated from the glTF material options alone)
	 * but reuse of the same glTF material may require multiple threejs materials
	 * to accommodate different primitive types, defines, etc. New materials will
	 * be created if necessary, and reused from a cache.
	 * @param  {Object3D} mesh Mesh, Line, or Points instance.
	 */
	assignFinalMaterial( mesh ) {

		const geometry = mesh.geometry;
		let material = mesh.material;

		const useDerivativeTangents = geometry.attributes.tangent === undefined;
		const useVertexColors = geometry.attributes.color !== undefined;
		const useFlatShading = geometry.attributes.normal === undefined;

		if ( mesh.isPoints ) {

			const cacheKey = 'PointsMaterial:' + material.uuid;

			let pointsMaterial = this.cache.get( cacheKey );

			if ( ! pointsMaterial ) {

				pointsMaterial = new PointsMaterial();
				Material.prototype.copy.call( pointsMaterial, material );
				pointsMaterial.color.copy( material.color );
				pointsMaterial.map = material.map;
				pointsMaterial.sizeAttenuation = false; // glTF spec says points should be 1px

				this.cache.add( cacheKey, pointsMaterial );

			}

			material = pointsMaterial;

		} else if ( mesh.isLine ) {

			const cacheKey = 'LineBasicMaterial:' + material.uuid;

			let lineMaterial = this.cache.get( cacheKey );

			if ( ! lineMaterial ) {

				lineMaterial = new LineBasicMaterial();
				Material.prototype.copy.call( lineMaterial, material );
				lineMaterial.color.copy( material.color );

				this.cache.add( cacheKey, lineMaterial );

			}

			material = lineMaterial;

		}

		// Clone the material if it will be modified
		if ( useDerivativeTangents || useVertexColors || useFlatShading ) {

			let cacheKey = 'ClonedMaterial:' + material.uuid + ':';

			if ( material.isGLTFSpecularGlossinessMaterial ) cacheKey += 'specular-glossiness:';
			if ( useDerivativeTangents ) cacheKey += 'derivative-tangents:';
			if ( useVertexColors ) cacheKey += 'vertex-colors:';
			if ( useFlatShading ) cacheKey += 'flat-shading:';

			let cachedMaterial = this.cache.get( cacheKey );

			if ( ! cachedMaterial ) {

				cachedMaterial = material.clone();

				if ( useVertexColors ) cachedMaterial.vertexColors = true;
				if ( useFlatShading ) cachedMaterial.flatShading = true;

				if ( useDerivativeTangents ) {

					// https://github.com/mrdoob/three.js/issues/11438#issuecomment-507003995
					if ( cachedMaterial.normalScale ) cachedMaterial.normalScale.y *= - 1;
					if ( cachedMaterial.clearcoatNormalScale ) cachedMaterial.clearcoatNormalScale.y *= - 1;

				}

				this.cache.add( cacheKey, cachedMaterial );

				this.associations.set( cachedMaterial, this.associations.get( material ) );

			}

			material = cachedMaterial;

		}

		// workarounds for mesh and geometry

		if ( material.aoMap && geometry.attributes.uv2 === undefined && geometry.attributes.uv !== undefined ) {

			geometry.setAttribute( 'uv2', geometry.attributes.uv );

		}

		mesh.material = material;

	}

	getMaterialType( /* materialIndex */ ) {

		return MeshStandardMaterial;

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#materials
	 * @param {number} materialIndex
	 * @return {Promise<Material>}
	 */
	loadMaterial( materialIndex ) {

		const parser = this;
		const json = this.json;
		const extensions = this.extensions;
		const materialDef = json.materials[ materialIndex ];

		let materialType;
		const materialParams = {};
		const materialExtensions = materialDef.extensions || {};

		const pending = [];

		if ( materialExtensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ] ) {

			const sgExtension = extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ];
			materialType = sgExtension.getMaterialType();
			pending.push( sgExtension.extendParams( materialParams, materialDef, parser ) );

		} else if ( materialExtensions[ EXTENSIONS.KHR_MATERIALS_UNLIT ] ) {

			const kmuExtension = extensions[ EXTENSIONS.KHR_MATERIALS_UNLIT ];
			materialType = kmuExtension.getMaterialType();
			pending.push( kmuExtension.extendParams( materialParams, materialDef, parser ) );

		} else {

			// Specification:
			// https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#metallic-roughness-material

			const metallicRoughness = materialDef.pbrMetallicRoughness || {};

			materialParams.color = new Color( 1.0, 1.0, 1.0 );
			materialParams.opacity = 1.0;

			if ( Array.isArray( metallicRoughness.baseColorFactor ) ) {

				const array = metallicRoughness.baseColorFactor;

				materialParams.color.fromArray( array );
				materialParams.opacity = array[ 3 ];

			}

			if ( metallicRoughness.baseColorTexture !== undefined ) {

				pending.push( parser.assignTexture( materialParams, 'map', metallicRoughness.baseColorTexture ) );

			}

			materialParams.metalness = metallicRoughness.metallicFactor !== undefined ? metallicRoughness.metallicFactor : 1.0;
			materialParams.roughness = metallicRoughness.roughnessFactor !== undefined ? metallicRoughness.roughnessFactor : 1.0;

			if ( metallicRoughness.metallicRoughnessTexture !== undefined ) {

				pending.push( parser.assignTexture( materialParams, 'metalnessMap', metallicRoughness.metallicRoughnessTexture ) );
				pending.push( parser.assignTexture( materialParams, 'roughnessMap', metallicRoughness.metallicRoughnessTexture ) );

			}

			materialType = this._invokeOne( function ( ext ) {

				return ext.getMaterialType && ext.getMaterialType( materialIndex );

			} );

			pending.push( Promise.all( this._invokeAll( function ( ext ) {

				return ext.extendMaterialParams && ext.extendMaterialParams( materialIndex, materialParams );

			} ) ) );

		}

		if ( materialDef.doubleSided === true ) {

			materialParams.side = DoubleSide;

		}

		const alphaMode = materialDef.alphaMode || ALPHA_MODES.OPAQUE;

		if ( alphaMode === ALPHA_MODES.BLEND ) {

			materialParams.transparent = true;

			// See: https://github.com/mrdoob/three.js/issues/17706
			materialParams.depthWrite = false;

		} else {

			materialParams.format = RGBFormat;
			materialParams.transparent = false;

			if ( alphaMode === ALPHA_MODES.MASK ) {

				materialParams.alphaTest = materialDef.alphaCutoff !== undefined ? materialDef.alphaCutoff : 0.5;

			}

		}

		if ( materialDef.normalTexture !== undefined && materialType !== MeshBasicMaterial ) {

			pending.push( parser.assignTexture( materialParams, 'normalMap', materialDef.normalTexture ) );

			materialParams.normalScale = new Vector2( 1, 1 );

			if ( materialDef.normalTexture.scale !== undefined ) {

				const scale = materialDef.normalTexture.scale;

				materialParams.normalScale.set( scale, scale );

			}

		}

		if ( materialDef.occlusionTexture !== undefined && materialType !== MeshBasicMaterial ) {

			pending.push( parser.assignTexture( materialParams, 'aoMap', materialDef.occlusionTexture ) );

			if ( materialDef.occlusionTexture.strength !== undefined ) {

				materialParams.aoMapIntensity = materialDef.occlusionTexture.strength;

			}

		}

		if ( materialDef.emissiveFactor !== undefined && materialType !== MeshBasicMaterial ) {

			materialParams.emissive = new Color().fromArray( materialDef.emissiveFactor );

		}

		if ( materialDef.emissiveTexture !== undefined && materialType !== MeshBasicMaterial ) {

			pending.push( parser.assignTexture( materialParams, 'emissiveMap', materialDef.emissiveTexture ) );

		}

		return Promise.all( pending ).then( function () {

			let material;

			if ( materialType === GLTFMeshStandardSGMaterial ) {

				material = extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ].createMaterial( materialParams );

			} else {

				material = new materialType( materialParams );

			}

			if ( materialDef.name ) material.name = materialDef.name;

			// baseColorTexture, emissiveTexture, and specularGlossinessTexture use sRGB encoding.
			if ( material.map ) material.map.encoding = sRGBEncoding;
			if ( material.emissiveMap ) material.emissiveMap.encoding = sRGBEncoding;

			assignExtrasToUserData( material, materialDef );

			parser.associations.set( material, { materials: materialIndex } );

			if ( materialDef.extensions ) addUnknownExtensionsToUserData( extensions, material, materialDef );

			return material;

		} );

	}

	/** When Object3D instances are targeted by animation, they need unique names. */
	createUniqueName( originalName ) {

		const sanitizedName = PropertyBinding.sanitizeNodeName( originalName || '' );

		let name = sanitizedName;

		for ( let i = 1; this.nodeNamesUsed[ name ]; ++ i ) {

			name = sanitizedName + '_' + i;

		}

		this.nodeNamesUsed[ name ] = true;

		return name;

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#geometry
	 *
	 * Creates BufferGeometries from primitives.
	 *
	 * @param {Array<GLTF.Primitive>} primitives
	 * @return {Promise<Array<BufferGeometry>>}
	 */
	loadGeometries( primitives ) {

		const parser = this;
		const extensions = this.extensions;
		const cache = this.primitiveCache;

		function createDracoPrimitive( primitive ) {

			return extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ]
				.decodePrimitive( primitive, parser )
				.then( function ( geometry ) {

					return addPrimitiveAttributes( geometry, primitive, parser );

				} );

		}

		const pending = [];

		for ( let i = 0, il = primitives.length; i < il; i ++ ) {

			const primitive = primitives[ i ];
			const cacheKey = createPrimitiveKey( primitive );

			// See if we've already created this geometry
			const cached = cache[ cacheKey ];

			if ( cached ) {

				// Use the cached geometry if it exists
				pending.push( cached.promise );

			} else {

				let geometryPromise;

				if ( primitive.extensions && primitive.extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ] ) {

					// Use DRACO geometry if available
					geometryPromise = createDracoPrimitive( primitive );

				} else {

					// Otherwise create a new geometry
					geometryPromise = addPrimitiveAttributes( new BufferGeometry(), primitive, parser );

				}

				// Cache this geometry
				cache[ cacheKey ] = { primitive: primitive, promise: geometryPromise };

				pending.push( geometryPromise );

			}

		}

		return Promise.all( pending );

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#meshes
	 * @param {number} meshIndex
	 * @return {Promise<Group|Mesh|SkinnedMesh>}
	 */
	loadMesh( meshIndex ) {

		const parser = this;
		const json = this.json;
		const extensions = this.extensions;

		const meshDef = json.meshes[ meshIndex ];
		const primitives = meshDef.primitives;

		const pending = [];

		for ( let i = 0, il = primitives.length; i < il; i ++ ) {

			const material = primitives[ i ].material === undefined
				? createDefaultMaterial( this.cache )
				: this.getDependency( 'material', primitives[ i ].material );

			pending.push( material );

		}

		pending.push( parser.loadGeometries( primitives ) );

		return Promise.all( pending ).then( function ( results ) {

			const materials = results.slice( 0, results.length - 1 );
			const geometries = results[ results.length - 1 ];

			const meshes = [];

			for ( let i = 0, il = geometries.length; i < il; i ++ ) {

				const geometry = geometries[ i ];
				const primitive = primitives[ i ];

				// 1. create Mesh

				let mesh;

				const material = materials[ i ];

				if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLES ||
						primitive.mode === WEBGL_CONSTANTS.TRIANGLE_STRIP ||
						primitive.mode === WEBGL_CONSTANTS.TRIANGLE_FAN ||
						primitive.mode === undefined ) {

					// .isSkinnedMesh isn't in glTF spec. See ._markDefs()
					mesh = meshDef.isSkinnedMesh === true
						? new SkinnedMesh( geometry, material )
						: new Mesh( geometry, material );

					if ( mesh.isSkinnedMesh === true && ! mesh.geometry.attributes.skinWeight.normalized ) {

						// we normalize floating point skin weight array to fix malformed assets (see #15319)
						// it's important to skip this for non-float32 data since normalizeSkinWeights assumes non-normalized inputs
						mesh.normalizeSkinWeights();

					}

					if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLE_STRIP ) {

						mesh.geometry = toTrianglesDrawMode( mesh.geometry, TriangleStripDrawMode );

					} else if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLE_FAN ) {

						mesh.geometry = toTrianglesDrawMode( mesh.geometry, TriangleFanDrawMode );

					}

				} else if ( primitive.mode === WEBGL_CONSTANTS.LINES ) {

					mesh = new LineSegments( geometry, material );

				} else if ( primitive.mode === WEBGL_CONSTANTS.LINE_STRIP ) {

					mesh = new Line( geometry, material );

				} else if ( primitive.mode === WEBGL_CONSTANTS.LINE_LOOP ) {

					mesh = new LineLoop( geometry, material );

				} else if ( primitive.mode === WEBGL_CONSTANTS.POINTS ) {

					mesh = new Points( geometry, material );

				} else {

					throw new Error( 'THREE.GLTFLoader: Primitive mode unsupported: ' + primitive.mode );

				}

				if ( Object.keys( mesh.geometry.morphAttributes ).length > 0 ) {

					updateMorphTargets( mesh, meshDef );

				}

				mesh.name = parser.createUniqueName( meshDef.name || ( 'mesh_' + meshIndex ) );

				assignExtrasToUserData( mesh, meshDef );

				if ( primitive.extensions ) addUnknownExtensionsToUserData( extensions, mesh, primitive );

				parser.assignFinalMaterial( mesh );

				meshes.push( mesh );

			}

			for ( let i = 0, il = meshes.length; i < il; i ++ ) {

				parser.associations.set( meshes[ i ], {
					meshes: meshIndex,
					primitives: i
				} );

			}

			if ( meshes.length === 1 ) {

				return meshes[ 0 ];

			}

			const group = new Group();

			parser.associations.set( group, { meshes: meshIndex } );

			for ( let i = 0, il = meshes.length; i < il; i ++ ) {

				group.add( meshes[ i ] );

			}

			return group;

		} );

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#cameras
	 * @param {number} cameraIndex
	 * @return {Promise<THREE.Camera>}
	 */
	loadCamera( cameraIndex ) {

		let camera;
		const cameraDef = this.json.cameras[ cameraIndex ];
		const params = cameraDef[ cameraDef.type ];

		if ( ! params ) {

			console.warn( 'THREE.GLTFLoader: Missing camera parameters.' );
			return;

		}

		if ( cameraDef.type === 'perspective' ) {

			camera = new PerspectiveCamera( MathUtils.radToDeg( params.yfov ), params.aspectRatio || 1, params.znear || 1, params.zfar || 2e6 );

		} else if ( cameraDef.type === 'orthographic' ) {

			camera = new OrthographicCamera( - params.xmag, params.xmag, params.ymag, - params.ymag, params.znear, params.zfar );

		}

		if ( cameraDef.name ) camera.name = this.createUniqueName( cameraDef.name );

		assignExtrasToUserData( camera, cameraDef );

		return Promise.resolve( camera );

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#skins
	 * @param {number} skinIndex
	 * @return {Promise<Object>}
	 */
	loadSkin( skinIndex ) {

		const skinDef = this.json.skins[ skinIndex ];

		const skinEntry = { joints: skinDef.joints };

		if ( skinDef.inverseBindMatrices === undefined ) {

			return Promise.resolve( skinEntry );

		}

		return this.getDependency( 'accessor', skinDef.inverseBindMatrices ).then( function ( accessor ) {

			skinEntry.inverseBindMatrices = accessor;

			return skinEntry;

		} );

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#animations
	 * @param {number} animationIndex
	 * @return {Promise<AnimationClip>}
	 */
	loadAnimation( animationIndex ) {

		const json = this.json;

		const animationDef = json.animations[ animationIndex ];

		const pendingNodes = [];
		const pendingInputAccessors = [];
		const pendingOutputAccessors = [];
		const pendingSamplers = [];
		const pendingTargets = [];

		for ( let i = 0, il = animationDef.channels.length; i < il; i ++ ) {

			const channel = animationDef.channels[ i ];
			const sampler = animationDef.samplers[ channel.sampler ];
			const target = channel.target;
			const name = target.node !== undefined ? target.node : target.id; // NOTE: target.id is deprecated.
			const input = animationDef.parameters !== undefined ? animationDef.parameters[ sampler.input ] : sampler.input;
			const output = animationDef.parameters !== undefined ? animationDef.parameters[ sampler.output ] : sampler.output;

			pendingNodes.push( this.getDependency( 'node', name ) );
			pendingInputAccessors.push( this.getDependency( 'accessor', input ) );
			pendingOutputAccessors.push( this.getDependency( 'accessor', output ) );
			pendingSamplers.push( sampler );
			pendingTargets.push( target );

		}

		return Promise.all( [

			Promise.all( pendingNodes ),
			Promise.all( pendingInputAccessors ),
			Promise.all( pendingOutputAccessors ),
			Promise.all( pendingSamplers ),
			Promise.all( pendingTargets )

		] ).then( function ( dependencies ) {

			const nodes = dependencies[ 0 ];
			const inputAccessors = dependencies[ 1 ];
			const outputAccessors = dependencies[ 2 ];
			const samplers = dependencies[ 3 ];
			const targets = dependencies[ 4 ];

			const tracks = [];

			for ( let i = 0, il = nodes.length; i < il; i ++ ) {

				const node = nodes[ i ];
				const inputAccessor = inputAccessors[ i ];
				const outputAccessor = outputAccessors[ i ];
				const sampler = samplers[ i ];
				const target = targets[ i ];

				if ( node === undefined ) continue;

				node.updateMatrix();
				node.matrixAutoUpdate = true;

				let TypedKeyframeTrack;

				switch ( PATH_PROPERTIES[ target.path ] ) {

					case PATH_PROPERTIES.weights:

						TypedKeyframeTrack = NumberKeyframeTrack;
						break;

					case PATH_PROPERTIES.rotation:

						TypedKeyframeTrack = QuaternionKeyframeTrack;
						break;

					case PATH_PROPERTIES.position:
					case PATH_PROPERTIES.scale:
					default:

						TypedKeyframeTrack = VectorKeyframeTrack;
						break;

				}

				const targetName = node.name ? node.name : node.uuid;

				const interpolation = sampler.interpolation !== undefined ? INTERPOLATION[ sampler.interpolation ] : InterpolateLinear;

				const targetNames = [];

				if ( PATH_PROPERTIES[ target.path ] === PATH_PROPERTIES.weights ) {

					// Node may be a Group (glTF mesh with several primitives) or a Mesh.
					node.traverse( function ( object ) {

						if ( object.isMesh === true && object.morphTargetInfluences ) {

							targetNames.push( object.name ? object.name : object.uuid );

						}

					} );

				} else {

					targetNames.push( targetName );

				}

				let outputArray = outputAccessor.array;

				if ( outputAccessor.normalized ) {

					const scale = getNormalizedComponentScale( outputArray.constructor );
					const scaled = new Float32Array( outputArray.length );

					for ( let j = 0, jl = outputArray.length; j < jl; j ++ ) {

						scaled[ j ] = outputArray[ j ] * scale;

					}

					outputArray = scaled;

				}

				for ( let j = 0, jl = targetNames.length; j < jl; j ++ ) {

					const track = new TypedKeyframeTrack(
						targetNames[ j ] + '.' + PATH_PROPERTIES[ target.path ],
						inputAccessor.array,
						outputArray,
						interpolation
					);

					// Override interpolation with custom factory method.
					if ( sampler.interpolation === 'CUBICSPLINE' ) {

						track.createInterpolant = function InterpolantFactoryMethodGLTFCubicSpline( result ) {

							// A CUBICSPLINE keyframe in glTF has three output values for each input value,
							// representing inTangent, splineVertex, and outTangent. As a result, track.getValueSize()
							// must be divided by three to get the interpolant's sampleSize argument.

							const interpolantType = ( this instanceof QuaternionKeyframeTrack ) ? GLTFCubicSplineQuaternionInterpolant : GLTFCubicSplineInterpolant;

							return new interpolantType( this.times, this.values, this.getValueSize() / 3, result );

						};

						// Mark as CUBICSPLINE. `track.getInterpolation()` doesn't support custom interpolants.
						track.createInterpolant.isInterpolantFactoryMethodGLTFCubicSpline = true;

					}

					tracks.push( track );

				}

			}

			const name = animationDef.name ? animationDef.name : 'animation_' + animationIndex;

			return new AnimationClip( name, undefined, tracks );

		} );

	}

	createNodeMesh( nodeIndex ) {

		const json = this.json;
		const parser = this;
		const nodeDef = json.nodes[ nodeIndex ];

		if ( nodeDef.mesh === undefined ) return null;

		return parser.getDependency( 'mesh', nodeDef.mesh ).then( function ( mesh ) {

			const node = parser._getNodeRef( parser.meshCache, nodeDef.mesh, mesh );

			// if weights are provided on the node, override weights on the mesh.
			if ( nodeDef.weights !== undefined ) {

				node.traverse( function ( o ) {

					if ( ! o.isMesh ) return;

					for ( let i = 0, il = nodeDef.weights.length; i < il; i ++ ) {

						o.morphTargetInfluences[ i ] = nodeDef.weights[ i ];

					}

				} );

			}

			return node;

		} );

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#nodes-and-hierarchy
	 * @param {number} nodeIndex
	 * @return {Promise<Object3D>}
	 */
	loadNode( nodeIndex ) {

		const json = this.json;
		const extensions = this.extensions;
		const parser = this;

		const nodeDef = json.nodes[ nodeIndex ];

		// reserve node's name before its dependencies, so the root has the intended name.
		const nodeName = nodeDef.name ? parser.createUniqueName( nodeDef.name ) : '';

		return ( function () {

			const pending = [];

			const meshPromise = parser._invokeOne( function ( ext ) {

				return ext.createNodeMesh && ext.createNodeMesh( nodeIndex );

			} );

			if ( meshPromise ) {

				pending.push( meshPromise );

			}

			if ( nodeDef.camera !== undefined ) {

				pending.push( parser.getDependency( 'camera', nodeDef.camera ).then( function ( camera ) {

					return parser._getNodeRef( parser.cameraCache, nodeDef.camera, camera );

				} ) );

			}

			parser._invokeAll( function ( ext ) {

				return ext.createNodeAttachment && ext.createNodeAttachment( nodeIndex );

			} ).forEach( function ( promise ) {

				pending.push( promise );

			} );

			return Promise.all( pending );

		}() ).then( function ( objects ) {

			let node;

			// .isBone isn't in glTF spec. See ._markDefs
			if ( nodeDef.isBone === true ) {

				node = new Bone();

			} else if ( objects.length > 1 ) {

				node = new Group();

			} else if ( objects.length === 1 ) {

				node = objects[ 0 ];

			} else {

				node = new Object3D();

			}

			if ( node !== objects[ 0 ] ) {

				for ( let i = 0, il = objects.length; i < il; i ++ ) {

					node.add( objects[ i ] );

				}

			}

			if ( nodeDef.name ) {

				node.userData.name = nodeDef.name;
				node.name = nodeName;

			}

			assignExtrasToUserData( node, nodeDef );

			if ( nodeDef.extensions ) addUnknownExtensionsToUserData( extensions, node, nodeDef );

			if ( nodeDef.matrix !== undefined ) {

				const matrix = new Matrix4();
				matrix.fromArray( nodeDef.matrix );
				node.applyMatrix4( matrix );

			} else {

				if ( nodeDef.translation !== undefined ) {

					node.position.fromArray( nodeDef.translation );

				}

				if ( nodeDef.rotation !== undefined ) {

					node.quaternion.fromArray( nodeDef.rotation );

				}

				if ( nodeDef.scale !== undefined ) {

					node.scale.fromArray( nodeDef.scale );

				}

			}

			if ( ! parser.associations.has( node ) ) {

				parser.associations.set( node, {} );

			}

			parser.associations.get( node ).nodes = nodeIndex;

			return node;

		} );

	}

	/**
	 * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#scenes
	 * @param {number} sceneIndex
	 * @return {Promise<Group>}
	 */
	loadScene( sceneIndex ) {

		const json = this.json;
		const extensions = this.extensions;
		const sceneDef = this.json.scenes[ sceneIndex ];
		const parser = this;

		// Loader returns Group, not Scene.
		// See: https://github.com/mrdoob/three.js/issues/18342#issuecomment-578981172
		const scene = new Group();
		if ( sceneDef.name ) scene.name = parser.createUniqueName( sceneDef.name );

		assignExtrasToUserData( scene, sceneDef );

		if ( sceneDef.extensions ) addUnknownExtensionsToUserData( extensions, scene, sceneDef );

		const nodeIds = sceneDef.nodes || [];

		const pending = [];

		for ( let i = 0, il = nodeIds.length; i < il; i ++ ) {

			pending.push( buildNodeHierarchy( nodeIds[ i ], scene, json, parser ) );

		}

		return Promise.all( pending ).then( function () {

			// Removes dangling associations, associations that reference a node that
			// didn't make it into the scene.
			const reduceAssociations = ( node ) => {

				const reducedAssociations = new Map();

				for ( const [ key, value ] of parser.associations ) {

					if ( key instanceof Material || key instanceof Texture ) {

						reducedAssociations.set( key, value );

					}

				}

				node.traverse( ( node ) => {

					const mappings = parser.associations.get( node );

					if ( mappings != null ) {

						reducedAssociations.set( node, mappings );

					}

				} );

				return reducedAssociations;

			};

			parser.associations = reduceAssociations( scene );

			return scene;

		} );

	}

}

function buildNodeHierarchy( nodeId, parentObject, json, parser ) {

	const nodeDef = json.nodes[ nodeId ];

	return parser.getDependency( 'node', nodeId ).then( function ( node ) {

		if ( nodeDef.skin === undefined ) return node;

		// build skeleton here as well

		let skinEntry;

		return parser.getDependency( 'skin', nodeDef.skin ).then( function ( skin ) {

			skinEntry = skin;

			const pendingJoints = [];

			for ( let i = 0, il = skinEntry.joints.length; i < il; i ++ ) {

				pendingJoints.push( parser.getDependency( 'node', skinEntry.joints[ i ] ) );

			}

			return Promise.all( pendingJoints );

		} ).then( function ( jointNodes ) {

			node.traverse( function ( mesh ) {

				if ( ! mesh.isMesh ) return;

				const bones = [];
				const boneInverses = [];

				for ( let j = 0, jl = jointNodes.length; j < jl; j ++ ) {

					const jointNode = jointNodes[ j ];

					if ( jointNode ) {

						bones.push( jointNode );

						const mat = new Matrix4();

						if ( skinEntry.inverseBindMatrices !== undefined ) {

							mat.fromArray( skinEntry.inverseBindMatrices.array, j * 16 );

						}

						boneInverses.push( mat );

					} else {

						console.warn( 'THREE.GLTFLoader: Joint "%s" could not be found.', skinEntry.joints[ j ] );

					}

				}

				mesh.bind( new Skeleton( bones, boneInverses ), mesh.matrixWorld );

			} );

			return node;

		} );

	} ).then( function ( node ) {

		// build node hierachy

		parentObject.add( node );

		const pending = [];

		if ( nodeDef.children ) {

			const children = nodeDef.children;

			for ( let i = 0, il = children.length; i < il; i ++ ) {

				const child = children[ i ];
				pending.push( buildNodeHierarchy( child, node, json, parser ) );

			}

		}

		return Promise.all( pending );

	} );

}

/**
 * @param {BufferGeometry} geometry
 * @param {GLTF.Primitive} primitiveDef
 * @param {GLTFParser} parser
 */
function computeBounds( geometry, primitiveDef, parser ) {

	const attributes = primitiveDef.attributes;

	const box = new Box3();

	if ( attributes.POSITION !== undefined ) {

		const accessor = parser.json.accessors[ attributes.POSITION ];

		const min = accessor.min;
		const max = accessor.max;

		// glTF requires 'min' and 'max', but VRM (which extends glTF) currently ignores that requirement.

		if ( min !== undefined && max !== undefined ) {

			box.set(
				new Vector3( min[ 0 ], min[ 1 ], min[ 2 ] ),
				new Vector3( max[ 0 ], max[ 1 ], max[ 2 ] )
			);

			if ( accessor.normalized ) {

				const boxScale = getNormalizedComponentScale( WEBGL_COMPONENT_TYPES[ accessor.componentType ] );
				box.min.multiplyScalar( boxScale );
				box.max.multiplyScalar( boxScale );

			}

		} else {

			console.warn( 'THREE.GLTFLoader: Missing min/max properties for accessor POSITION.' );

			return;

		}

	} else {

		return;

	}

	const targets = primitiveDef.targets;

	if ( targets !== undefined ) {

		const maxDisplacement = new Vector3();
		const vector = new Vector3();

		for ( let i = 0, il = targets.length; i < il; i ++ ) {

			const target = targets[ i ];

			if ( target.POSITION !== undefined ) {

				const accessor = parser.json.accessors[ target.POSITION ];
				const min = accessor.min;
				const max = accessor.max;

				// glTF requires 'min' and 'max', but VRM (which extends glTF) currently ignores that requirement.

				if ( min !== undefined && max !== undefined ) {

					// we need to get max of absolute components because target weight is [-1,1]
					vector.setX( Math.max( Math.abs( min[ 0 ] ), Math.abs( max[ 0 ] ) ) );
					vector.setY( Math.max( Math.abs( min[ 1 ] ), Math.abs( max[ 1 ] ) ) );
					vector.setZ( Math.max( Math.abs( min[ 2 ] ), Math.abs( max[ 2 ] ) ) );


					if ( accessor.normalized ) {

						const boxScale = getNormalizedComponentScale( WEBGL_COMPONENT_TYPES[ accessor.componentType ] );
						vector.multiplyScalar( boxScale );

					}

					// Note: this assumes that the sum of all weights is at most 1. This isn't quite correct - it's more conservative
					// to assume that each target can have a max weight of 1. However, for some use cases - notably, when morph targets
					// are used to implement key-frame animations and as such only two are active at a time - this results in very large
					// boxes. So for now we make a box that's sometimes a touch too small but is hopefully mostly of reasonable size.
					maxDisplacement.max( vector );

				} else {

					console.warn( 'THREE.GLTFLoader: Missing min/max properties for accessor POSITION.' );

				}

			}

		}

		// As per comment above this box isn't conservative, but has a reasonable size for a very large number of morph targets.
		box.expandByVector( maxDisplacement );

	}

	geometry.boundingBox = box;

	const sphere = new Sphere();

	box.getCenter( sphere.center );
	sphere.radius = box.min.distanceTo( box.max ) / 2;

	geometry.boundingSphere = sphere;

}

/**
 * @param {BufferGeometry} geometry
 * @param {GLTF.Primitive} primitiveDef
 * @param {GLTFParser} parser
 * @return {Promise<BufferGeometry>}
 */
function addPrimitiveAttributes( geometry, primitiveDef, parser ) {

	const attributes = primitiveDef.attributes;

	const pending = [];

	function assignAttributeAccessor( accessorIndex, attributeName ) {

		return parser.getDependency( 'accessor', accessorIndex )
			.then( function ( accessor ) {

				geometry.setAttribute( attributeName, accessor );

			} );

	}

	for ( const gltfAttributeName in attributes ) {

		const threeAttributeName = ATTRIBUTES[ gltfAttributeName ] || gltfAttributeName.toLowerCase();

		// Skip attributes already provided by e.g. Draco extension.
		if ( threeAttributeName in geometry.attributes ) continue;

		pending.push( assignAttributeAccessor( attributes[ gltfAttributeName ], threeAttributeName ) );

	}

	if ( primitiveDef.indices !== undefined && ! geometry.index ) {

		const accessor = parser.getDependency( 'accessor', primitiveDef.indices ).then( function ( accessor ) {

			geometry.setIndex( accessor );

		} );

		pending.push( accessor );

	}

	assignExtrasToUserData( geometry, primitiveDef );

	computeBounds( geometry, primitiveDef, parser );

	return Promise.all( pending ).then( function () {

		return primitiveDef.targets !== undefined
			? addMorphTargets( geometry, primitiveDef.targets, parser )
			: geometry;

	} );

}

/**
 * @param {BufferGeometry} geometry
 * @param {Number} drawMode
 * @return {BufferGeometry}
 */
function toTrianglesDrawMode( geometry, drawMode ) {

	let index = geometry.getIndex();

	// generate index if not present

	if ( index === null ) {

		const indices = [];

		const position = geometry.getAttribute( 'position' );

		if ( position !== undefined ) {

			for ( let i = 0; i < position.count; i ++ ) {

				indices.push( i );

			}

			geometry.setIndex( indices );
			index = geometry.getIndex();

		} else {

			console.error( 'THREE.GLTFLoader.toTrianglesDrawMode(): Undefined position attribute. Processing not possible.' );
			return geometry;

		}

	}

	//

	const numberOfTriangles = index.count - 2;
	const newIndices = [];

	if ( drawMode === TriangleFanDrawMode ) {

		// gl.TRIANGLE_FAN

		for ( let i = 1; i <= numberOfTriangles; i ++ ) {

			newIndices.push( index.getX( 0 ) );
			newIndices.push( index.getX( i ) );
			newIndices.push( index.getX( i + 1 ) );

		}

	} else {

		// gl.TRIANGLE_STRIP

		for ( let i = 0; i < numberOfTriangles; i ++ ) {

			if ( i % 2 === 0 ) {

				newIndices.push( index.getX( i ) );
				newIndices.push( index.getX( i + 1 ) );
				newIndices.push( index.getX( i + 2 ) );


			} else {

				newIndices.push( index.getX( i + 2 ) );
				newIndices.push( index.getX( i + 1 ) );
				newIndices.push( index.getX( i ) );

			}

		}

	}

	if ( ( newIndices.length / 3 ) !== numberOfTriangles ) {

		console.error( 'THREE.GLTFLoader.toTrianglesDrawMode(): Unable to generate correct amount of triangles.' );

	}

	// build final geometry

	const newGeometry = geometry.clone();
	newGeometry.setIndex( newIndices );

	return newGeometry;

}

export { GLTFLoader };